This book provides pregnant women and new parents with evidence-based information on pregnancy and parenting. Most paren
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English Pages [261] Year 2021
Table of contents :
Preface
How to Read the Book
Acknowledgments
Contents
About the Author
Part I: Science and Parenting
Chapter 1: Does a “Good” Parent Need Science?
What Is Science?
Scientific Inference
Experiments vs Observational Studies
Bias and Precision
Does a “Good” Parent Need Science?
Chapter 2: Summing Up: Synthesizing the Scientific Evidence
Why Synthesize the Evidence?
Systematic Review
Reviewing the Evidence on Parenting
How to Read the Rest of This Book
Part II: Pregnancy
Preface
Chapter 3: How Much Should You Weigh?
Introduction
Pre-Pregnancy Body Mass Index (BMI)
Gestational Weight Gain (GWG)
**Detailed Assessment
Research Design Issues
Pre-pregnancy Body Mass Index (BMI)
Gestational Weight Gain (GWG)
Evidence-Based Recommendations
What’s Next?
References
Chapter 4: What Should You Eat?
Introduction
**Detailed Assessment
Research Design Issues
Macronutrient (Energy, Protein, Carbohydrate, and Fat) Intake
Micronutrient Intake
Iron
Folic Acid
Vitamins C and E
Calcium
Vitamin D
Multiple Micronutrients
Omega-3 Fatty Acids
Foodborne Microorganisms
Listeria
Toxoplasma
Evidence-Based Recommendations
What’s Next?
References
Chapter 5: Work and Exercise in Pregnancy
Introduction
**Detailed Assessment
Physically Demanding Work
Aerobic Exercise
Yoga
Pelvic Floor Exercises
Evidence-Based Recommendations
What’s Next?
References
Chapter 6: Tobacco, Alcohol, and Drugs in Pregnancy
Introduction
**Detailed Assessment
Research Design Issues
Maternal Smoking
Maternal Exposure to Environmental Tobacco Smoke (ETS)
Alcohol Consumption
Caffeine
Marijuana
Cocaine
Amphetamine and Methamphetamine
Opioids
Hallucinogens: LSD, Magic Mushrooms, Phencyclidine, and Ecstasy
Evidence-Based Recommendations
What’s Next?
References
Chapter 7: Medications in Pregnancy
Introduction
**Detailed Assessment
Pain Relievers: Acetaminophen and Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)
Antihistamines and Decongestants
Antacids
Oral Antibiotics
Antihypertensives: Drugs Taken Regularly for High Blood Pressure
Medications for Diabetes
Asthma Medications
Medications for Anxiety or Depression
Evidence-Based Recommendations
What’s Next?
References
Chapter 8: Vaccines in Pregnancy
Introduction
Tetanus
Pertussis (Whooping Cough)
Influenza
Coronavirus (COVID-19)
Evidence-Based Recommendations
References
Part III: Infancy and Toddlerhood
Chapter 9: Feeding Your Baby
Introduction
**Detailed Assessment
Research Design Issues
Breastfeeding vs Formula Feeding
Infection
Allergic Disease
Obesity, Diabetes, Heart Disease, and Stroke
Cancer
Dental Caries (Cavities)
Brain Development
Mental Health
Growth
Summary
Maternal Nutrition, Exercise, and Medication During Lactation (Breastfeeding)
Diet and Nutrition
Exercise
Alcohol and Cannabis
Medication
Types of Infant Formulas
Complementary Foods and Liquids
Liquids
Solid Foods: Types and Timing
Obesity
Food Allergies and Other Allergic Diseases
Brain Development
Micronutrient Supplementation
Evidence-Based Recommendations
What’s Next?
References
Chapter 10: Soothing Your Colicky Baby
Introduction
Effects of Treatment
Evidence-Based Recommendations
What’s Next?
References
Chapter 11: Should Your Baby Be Vaccinated?
Introduction
Evidence on Suspected Adverse Effects of Childhood Vaccines
**Detailed Assessment
Paralytic Polio and Polio Vaccine
Inconsolable Crying and Pertussis Vaccine
Intussusception and Rotavirus Vaccine
Autism and Vaccination
Adverse Immunological Effects of Multiple Vaccines
Summary
Evidence-Based Recommendations
What’s Next?
References
Chapter 12: Your Baby’s Sleep
Introduction
**Detailed Assessment
What Factors Influence Your Baby’s Sleep?
Infant Feeding
Sleeping Arrangement
Sleep Position
Noise and Light
Pacifiers
Babies’ Sleep and Later Health
What Interventions Improve Your Baby’s Sleep?
Types of Intervention
Do These Interventions Work? Do They Have Adverse Effects?
Evidence-Based Recommendations
What’s Next?
References
Chapter 13: Helping Your Baby’s Brain Develop
Introduction
**Detailed Assessment
Early Predictors of Language Acquisition and Cognitive Ability
Interventions to Improve Brain Development
Remediation Trials
Interventions in Children Not at High Risk
Evidence-Based Recommendations
What’s Next?
References
Chapter 14: Toilet Training Your Child
Introduction
The Four Questions of Toilet Training: What? Why? When? and How?
**Detailed Assessment
When? Studies of Age at Toilet Training
How? Studies of Methods of Toilet Training
Evidence-Based Recommendations
What’s Next?
References
Part IV: Childhood and Adolescence
Chapter 15: Disciplining Your Child
Introduction
Description of Disciplinary Approaches
Extinction
Positive Reinforcement
Negative Reinforcement
Time Out
**Detailed Assessment
Geographic, Cultural, and Temporal Variation in Disciplinary Approaches
What Works? A Review of the Evidence on Disciplinary Approaches
Research Design Issues
Evidence on Benefits and Harms
Evidence-Based Recommendations
What’s Next?
References
Chapter 16: What Should Your Child Eat?
Introduction
Global Variations and Trends in Child BMI and Obesity
Social and Familial Causes of Child Obesity
Why Prevent Obesity?
Outline of the Topics to Be Covered
**Detailed Assessment
Setting the Parameters
Research Design Issues
Dietary Interventions to Prevent Obesity
General Home-Based Dietary Interventions
Fruit and Vegetable Intake
Milk and Other Dairy Products
Sugar-Sweetened Beverages
Fat Intake
Candy Consumption
Carbohydrate Intake
Sleep Duration
Nutritional Interventions Designed to Achieve Outcomes Other Than Obesity Prevention
Micronutrient Intake
Iron
Zinc
Vitamin A
Vitamin D
Omega-3 Fatty Acids
Other Interventions
Breakfast
Probiotics
Evidence-Based Recommendations
What’s Next?
References
Chapter 17: Encouraging Your Child to Be Physically Active
Introduction
Why Is Physical Activity Important?
Changes in Physical Activity with Age
Geographic Variations and Temporal Trends
**Detailed Assessment
What Interventions Increase Children’s Physical Activity?
Interventions to Increase Overall Physical Activity
Walking or Cycling to and from School
“Digital” Interventions
Interventions to Reduce Sedentary Behavior
Will Exercise Prevent Your Child from Getting Fat?
Will Exercise Prevent Your Child from Developing High Blood Pressure, Heart Disease, or Diabetes?
Will Exercise Strengthen Your Child’s Bones?
Does Exercise Make Your Child Smarter?
Short-Term Exercise Bouts
Longer-Term Exercise and Fitness
Screen Time and Other Sedentary Behaviors
Does Exercise Improve Your Child’s Mental Health?
Summary
Evidence-Based Recommendations
References
Reference Tools
Glossary
Other Tools
Index
BEYOND PARENTING ADVICE
Michael S. Kramer, MD
Beyond Parenting Advice
Michael S. Kramer
Beyond Parenting Advice How Science Should Guide Your Decisions on Pregnancy and Child-Rearing
Michael S. Kramer, MD Faculty of Medicine McGill University Montreal, QC Canada
ISBN 978-3-030-74764-0 ISBN 978-3-030-74765-7 (eBook) https://doi.org/10.1007/978-3-030-74765-7 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Copernicus imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland
Preface
Poetry has done enough when it charms, but prose must also convince. —H. L. Mencken
A personal anecdote should help the reader of this book understand why I wrote it. In 1984, I began my first sabbatical leave from McGill University, spent at the World Health Organization in Geneva, Switzerland. My wife Claire and I had been married only 3 years, had no children yet, and were excited to live in the heart of Europe, surrounded by beautiful mountains. I went to the World Health Organization with the intention of extending my breastfeeding research to low- and middle-income countries. When I arrived there, however, the Head of the Maternal and Child Health Unit explained that the Unit had already done quite a lot of work on breastfeeding. He wanted to do far more in the area of low birth weight and asked me to consider spending my year there getting “on top of” that area. As a pediatrician, I knew something about low birth weight, but becoming an expert on research in its causes and prevention was a daunting challenge. Nonetheless, I accepted. Over the course of my sabbatical work, I was up to my neck with a systematic review of the published literature on the causes of low birth weight. By the end of the year (late 1985), I probably knew as much as anyone in the world about the topic. Less than a year later, Claire was pregnant with Eric, our first child. Claire asked me many questions about her pregnancy, but the one that stood out for me was about alcohol consumption. My systematic review of the published literature had found no evidence of any detectable risks with drinking up to two drinks a day during pregnancy, so to “play it safe,” I advised my wife to limit herself to one drink (glass of wine or beer with supper) per day. Most of the clinical and public health guidelines at the time advised pregnant women, and even women attempting to get pregnant, to avoid any alcohol consumption. Fortunately, Claire’s obstetrician did not follow those guidelines and did not proscribe modest alcohol use in her pregnant patients. Claire (and her obstetrician) resumed that sensible policy during her second and third pregnancies, and so did our daughter Elise when she became pregnant a few years ago with our v
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grandson Emmanuel. Thirty years after Claire’s first pregnancy with Eric, Elise was blessed (cursed?) with a stubborn father and an open-minded, well-informed obstetrician, both of whom supported her decision to have a glass of wine with her dinner every evening throughout her pregnancy. I had transmitted the same information and advice 5 years earlier to Sarah, my daughter-in-law and my son Eric’s wife, who was pregnant with our first grandson in 2011. Her reaction was different from Elise’s: she was unwilling to take the risk of drinking alcohol, except for small quantities on rare occasions. She probably ran a greater risk every time she crossed the street or got into a car. But for her, it was important to avoid those risks that she was reasonably able to control. Not crossing the street and not getting into a car for the duration of pregnancy were not acceptable options for her, but avoiding alcohol was. This book is written for Elise, but also for Sarah and for other parents like them. To my knowledge, it is the only book that systematically reviews the evidence on key decision choices faced by pregnant women and parents. I evaluate the quality of the published scientific evidence bearing on those choices and attempt to estimate their risks and benefits, as well as the uncertainty of the estimates. The risk and benefit estimates are statistical probabilities based on population averages, but they also need to be valued by the decision maker (the pregnant woman or parent, in this case) and stacked up against the effort and financial costs incurred by the decision. Faced with the same evidence, Elise and Sarah made different decisions about regular, light alcohol drinking during their pregnancies. Armed with the information provided in this book, other readers will also make different decisions. But those decisions will be informed decisions—not blind obedience to a book, blog, health provider, other “expert,” friends, family, or public health authority. Many pregnant women and new parents consult their obstetricians, midwives, pediatricians, or family doctors about what they should or should not do when faced with parenting decisions. Most of those clinicians base their advice on what they themselves were taught or on their own previous experience. But be warned: practicing clinicians are very unlikely to be familiar with the evidence I review in this book. How do I know that? I have presented several of the topics (chapters) reviewed in this book at educational seminars for academic obstetricians and gave them the same Pre-Reading Quiz Questions I use in my book. The majority of the attendees gave the wrong answer before my seminar, but all gave the correct answer after the seminar. I can also assure you that, as an academic pediatrician with a long-standing epidemiologic research career who practiced general pediatrics for 25 years, I myself was completely unaware of most of the evidence I review in the book. Clinical practitioners are generally far more concerned with keeping up to date with diagnostic tests, new treatments, and the management of serious clinical illnesses and complications. Examples include when to perform labor induction or cesarean delivery in a pregnant woman; whether to order a chest X-ray in a child with a cough, or a spinal tap in a baby with fever; and which antibiotic to prescribe for a woman or child with a urinary tract infection. The evidence they need is focused on the clinical decisions they make—not on the meat-and-potatoes,
Preface
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everyday decisions that you make as parents. Simply put, practicing clinicians are rarely trained in, and almost never keep up to date with, the science of parenting. The up-to-date aspect of the evidence base merits additional comment. I can assure you that by the time you read this book, some of its content will be out of date. In the year and a half between the time I began (early 2019) and completed (late 2020) this book, I felt obliged to update my literature search. Although the changes were not earth-shattering, the result was a substantial revision of the text and citation of new references. The transience of knowledge should not discourage you, however; it lies at the very heart of science. If substantial increases in knowledge occur over 18 months, think how out of date your doctor is! Advice is often based on belief or “tradition.” Parents who don’t trust the advice from their doctors or other health providers often look elsewhere. Advice is both cheap and plentiful—often only a click away. But when two or more websites, books, “experts,” or other sources completely contradict one another, how is the thinking parent to decide which advice to follow? In the era of fake news, alternative facts, and contradictory expert advice, more and more parents will prefer an objective, scientific rationale for their decisions—even if that rationale is out of date. If you are such a parent, this book is written for you. Moreover, the skills you acquire in reading this book will help you throughout your life in critically evaluating new information relevant to other areas of health, science, and technology.
How to Read the Book This book does not cover every conceivable topic relevant to pregnancy, infancy, and childhood. Instead, it focuses on key parental decisions for which advice and information are abundant but conflicting. The book’s contents are organized into four sections: an initial section comprising two introductory chapters and one section each devoted to topics on pregnancy, infancy and toddlerhood (the first 2–3 years of life), and childhood and adolescence. Each topic is limited to one chapter. A Reference Tools guide at the end of the book provides a glossary and reproduces a diagram (Fig. 1.1) and two tables (Tables 1.1 and 2.1. ) for easy consultation to refresh your memory about the meaning of unfamiliar words and concepts discussed in greater detail in Chaps. 1 and 2. Chapters 1 and 2 are short but dense. They are essential, however, to understand the scientific concepts and vocabulary used in the evidence review of each topic area. After reading the two initial chapters, the rest of the book can be used like an encyclopedia. In other words, you should be able to read and understand any later chapter in the book, or even a short section from any chapter. Despite the chronological order of pregnancy and the aging child, the topic chapters in Parts II, III, and IV could have been written, and can be read, in any order. Readers of any of the chapters in the pregnancy section should first read the Preface to the Pregnancy
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Section, because that Preface lists and explains the pregnancy outcomes shared by all of the pregnancy chapters. The evidence reviews that comprise Parts II, III, and IV share a common structure. Each begins with a Pre-Reading Quiz Question, followed by an Introduction that provides a historical, global, and biological context for the broad topic under review and an outline of the specific areas of evidence to be reviewed in detail later in the chapter. The Introduction is followed by a brief summary of the Key Points based on the available evidence and the correct answer to the Pre-Reading Quiz Question. For many of you, that is all you will want or need to read. For those who wish an in-depth review of each topic, as well as citations of the systematic reviews or individual studies that constitute the evidence base, those are contained in the Detailed Assessment section that follows the Key Points in all but the briefest chapters (Chaps. 8 and 10). After the Detailed Assessment, I offer evidence-based recommendations that flow from the assessment and that should influence your parenting decisions. Readers who skip the Detailed Assessment (which is marked in each chapter by a double asterisk**) will probably want to read the Evidence-Based Recommendations section near the end of the chapter.
Montreal, QC, Canada Michael S. Kramer, MD
Acknowledgments
I received encouragement and valuable advice from many persons in planning, organizing, writing, and editing this book. These persons include colleagues at McGill University and the University of Singapore, as well as family and friends. I would particularly like to cite a few of them: My wife Claire not only supported the need for the book, but also read every word. Although untrained in science, she is an experienced mother and unabashed but constructive critic. She made many insightful suggestions about how to “translate” difficult scientific concepts into language that is accessible to educated lay readers. My daughter Elise is a practicing optometrist who excels at expressing complex medical concepts in terms that her patients and the general public can understand. She too read every word of the book and suggested major improvements in content and style. Betsy Berliner is a PhD molecular biologist, experienced mother, and long-time friend who helped me integrate some of the technical and subject area content. All illustrations in the book are original drawings by Ms. Lea Kron. Ms. Tanya Sasportas helped create the design of the book cover.
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Contents
Part I Science and Parenting 1 Does a “Good” Parent Need Science?���������������������������������������������������� 3 What Is Science?�������������������������������������������������������������������������������������� 3 Scientific Inference���������������������������������������������������������������������������������� 5 Experiments vs Observational Studies���������������������������������������������������� 6 Bias and Precision������������������������������������������������������������������������������������ 8 Does a “Good” Parent Need Science? ���������������������������������������������������� 9 2 Summing Up: Synthesizing the Scientific Evidence����������������������������� 11 Why Synthesize the Evidence?���������������������������������������������������������������� 11 Systematic Review ���������������������������������������������������������������������������������� 12 Reviewing the Evidence on Parenting ���������������������������������������������������� 13 How to Read the Rest of This Book�������������������������������������������������������� 16 Part II Pregnancy 3 How Much Should You Weigh?�������������������������������������������������������������� 21 Introduction���������������������������������������������������������������������������������������������� 22 Pre-Pregnancy Body Mass Index (BMI)���������������������������������������������� 22 Gestational Weight Gain (GWG) �������������������������������������������������������� 23 **Detailed Assessment���������������������������������������������������������������������������� 24 Research Design Issues������������������������������������������������������������������������ 24 Pre-pregnancy Body Mass Index (BMI)���������������������������������������������� 25 Gestational Weight Gain (GWG) �������������������������������������������������������� 26 Evidence-Based Recommendations�������������������������������������������������������� 28 What’s Next?�������������������������������������������������������������������������������������������� 29 References������������������������������������������������������������������������������������������������ 29 4 What Should You Eat?���������������������������������������������������������������������������� 31 Introduction���������������������������������������������������������������������������������������������� 31 **Detailed Assessment���������������������������������������������������������������������������� 33 Research Design Issues������������������������������������������������������������������������ 33 xi
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Macronutrient (Energy, Protein, Carbohydrate, and Fat) Intake���������� 34 Micronutrient Intake���������������������������������������������������������������������������� 35 Foodborne Microorganisms ���������������������������������������������������������������� 40 Evidence-Based Recommendations�������������������������������������������������������� 42 What’s Next?�������������������������������������������������������������������������������������������� 42 References������������������������������������������������������������������������������������������������ 43 5 Work and Exercise in Pregnancy������������������������������������������������������������ 45 Introduction���������������������������������������������������������������������������������������������� 46 **Detailed Assessment���������������������������������������������������������������������������� 48 Physically Demanding Work���������������������������������������������������������������� 48 Aerobic Exercise���������������������������������������������������������������������������������� 49 Yoga ���������������������������������������������������������������������������������������������������� 49 Pelvic Floor Exercises�������������������������������������������������������������������������� 49 Evidence-Based Recommendations�������������������������������������������������������� 50 What’s Next?�������������������������������������������������������������������������������������������� 51 References������������������������������������������������������������������������������������������������ 51 6 Tobacco, Alcohol, and Drugs in Pregnancy ������������������������������������������ 53 Introduction���������������������������������������������������������������������������������������������� 53 **Detailed Assessment���������������������������������������������������������������������������� 55 Research Design Issues������������������������������������������������������������������������ 55 Maternal Smoking�������������������������������������������������������������������������������� 56 Maternal Exposure to Environmental Tobacco Smoke (ETS) ������������ 60 Alcohol Consumption�������������������������������������������������������������������������� 61 Caffeine������������������������������������������������������������������������������������������������ 63 Marijuana �������������������������������������������������������������������������������������������� 64 Cocaine������������������������������������������������������������������������������������������������ 65 Amphetamine and Methamphetamine ������������������������������������������������ 65 Opioids������������������������������������������������������������������������������������������������ 66 Hallucinogens: LSD, Magic Mushrooms, Phencyclidine, and Ecstasy 67 Evidence-Based Recommendations�������������������������������������������������������� 68 What’s Next?�������������������������������������������������������������������������������������������� 68 References������������������������������������������������������������������������������������������������ 68 7 Medications in Pregnancy ���������������������������������������������������������������������� 73 Introduction���������������������������������������������������������������������������������������������� 73 **Detailed Assessment���������������������������������������������������������������������������� 75 Pain Relievers: Acetaminophen and Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)����������������������������������������������������������������������������� 75 Antihistamines and Decongestants������������������������������������������������������ 78 Antacids ���������������������������������������������������������������������������������������������� 79 Oral Antibiotics������������������������������������������������������������������������������������ 79 Antihypertensives: Drugs Taken Regularly for High Blood Pressure 82 Medications for Diabetes �������������������������������������������������������������������� 83
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Asthma Medications���������������������������������������������������������������������������� 85 Medications for Anxiety or Depression ���������������������������������������������� 86 Evidence-Based Recommendations�������������������������������������������������������� 88 What’s Next?�������������������������������������������������������������������������������������������� 88 References������������������������������������������������������������������������������������������������ 88 8 Vaccines in Pregnancy ���������������������������������������������������������������������������� 91 Introduction���������������������������������������������������������������������������������������������� 91 Tetanus ���������������������������������������������������������������������������������������������������� 92 Pertussis (Whooping Cough) ������������������������������������������������������������������ 93 Influenza�������������������������������������������������������������������������������������������������� 94 Coronavirus (COVID-19)������������������������������������������������������������������������ 95 Evidence-Based Recommendations�������������������������������������������������������� 96 References������������������������������������������������������������������������������������������������ 96 Part III Infancy and Toddlerhood 9 Feeding Your Baby ���������������������������������������������������������������������������������� 99 Introduction���������������������������������������������������������������������������������������������� 100 **Detailed Assessment���������������������������������������������������������������������������� 102 Research Design Issues������������������������������������������������������������������������ 102 Breastfeeding vs Formula Feeding������������������������������������������������������ 103 Maternal Nutrition, Exercise, and Medication During Lactation (Breastfeeding)�������������������������������������������������������������������������������� 111 Types of Infant Formulas �������������������������������������������������������������������� 113 Complementary Foods and Liquids ���������������������������������������������������� 114 Micronutrient Supplementation ���������������������������������������������������������� 118 Evidence-Based Recommendations�������������������������������������������������������� 119 What’s Next?�������������������������������������������������������������������������������������������� 119 References������������������������������������������������������������������������������������������������ 120 10 Soothing Your Colicky Baby ������������������������������������������������������������������ 125 Introduction���������������������������������������������������������������������������������������������� 125 Effects of Treatment�������������������������������������������������������������������������������� 127 Evidence-Based Recommendations�������������������������������������������������������� 129 What’s Next?�������������������������������������������������������������������������������������������� 129 References������������������������������������������������������������������������������������������������ 129 11 Should Your Baby Be Vaccinated? �������������������������������������������������������� 131 Introduction���������������������������������������������������������������������������������������������� 132 Evidence on Suspected Adverse Effects of Childhood Vaccines������������ 134 **Detailed Assessment���������������������������������������������������������������������������� 136 Paralytic Polio and Polio Vaccine�������������������������������������������������������� 136 Inconsolable Crying and Pertussis Vaccine����������������������������������������� 138 Intussusception and Rotavirus Vaccine������������������������������������������������ 139 Autism and Vaccination ���������������������������������������������������������������������� 140
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Adverse Immunological Effects of Multiple Vaccines������������������������ 141 Summary���������������������������������������������������������������������������������������������� 143 Evidence-Based Recommendations�������������������������������������������������������� 143 What’s Next?�������������������������������������������������������������������������������������������� 143 References������������������������������������������������������������������������������������������������ 144 12 Your Baby’s Sleep������������������������������������������������������������������������������������ 147 Introduction���������������������������������������������������������������������������������������������� 148 **Detailed Assessment���������������������������������������������������������������������������� 150 What Factors Influence Your Baby’s Sleep?���������������������������������������� 150 Babies’ Sleep and Later Health������������������������������������������������������������ 155 What Interventions Improve Your Baby’s Sleep?�������������������������������� 156 Types of Intervention �������������������������������������������������������������������������� 157 Do These Interventions Work? Do They Have Adverse Effects?�������� 158 Evidence-Based Recommendations�������������������������������������������������������� 160 What’s Next?�������������������������������������������������������������������������������������������� 160 References������������������������������������������������������������������������������������������������ 161 13 Helping Your Baby’s Brain Develop������������������������������������������������������ 163 Introduction���������������������������������������������������������������������������������������������� 164 **Detailed Assessment���������������������������������������������������������������������������� 166 Early Predictors of Language Acquisition and Cognitive Ability�������� 166 Interventions to Improve Brain Development�������������������������������������� 168 Remediation Trials ������������������������������������������������������������������������������ 169 Interventions in Children Not at High Risk ���������������������������������������� 170 Evidence-Based Recommendations�������������������������������������������������������� 172 What’s Next?�������������������������������������������������������������������������������������������� 172 References������������������������������������������������������������������������������������������������ 173 14 Toilet Training Your Child���������������������������������������������������������������������� 175 Introduction���������������������������������������������������������������������������������������������� 176 The Four Questions of Toilet Training: What? Why? When? and How?�������������������������������������������������������������������������� 177 **Detailed Assessment���������������������������������������������������������������������������� 179 When? Studies of Age at Toilet Training �������������������������������������������� 180 How? Studies of Methods of Toilet Training�������������������������������������� 181 Evidence-Based Recommendations�������������������������������������������������������� 183 What’s Next?�������������������������������������������������������������������������������������������� 184 References������������������������������������������������������������������������������������������������ 184 Part IV Childhood and Adolescence 15 Disciplining Your Child �������������������������������������������������������������������������� 189 Introduction���������������������������������������������������������������������������������������������� 190 Description of Disciplinary Approaches���������������������������������������������� 191 **Detailed Assessment���������������������������������������������������������������������������� 194
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Geographic, Cultural, and Temporal Variation in Disciplinary Approaches�������������������������������������������������������������������������������������� 194 What Works? A Review of the Evidence on Disciplinary Approaches ���������������������������������������������������������������� 196 Research Design Issues������������������������������������������������������������������������ 196 Evidence on Benefits and Harms �������������������������������������������������������� 197 Evidence-Based Recommendations�������������������������������������������������������� 198 What’s Next?�������������������������������������������������������������������������������������������� 199 References������������������������������������������������������������������������������������������������ 200 16 What Should Your Child Eat?���������������������������������������������������������������� 201 Introduction���������������������������������������������������������������������������������������������� 202 Global Variations and Trends in Child BMI and Obesity�������������������� 203 Social and Familial Causes of Child Obesity�������������������������������������� 204 Why Prevent Obesity?������������������������������������������������������������������������� 205 Outline of the Topics to Be Covered�������������������������������������������������������� 206 **Detailed Assessment���������������������������������������������������������������������������� 207 Setting the Parameters�������������������������������������������������������������������������� 207 Research Design Issues������������������������������������������������������������������������ 208 Dietary Interventions to Prevent Obesity�������������������������������������������� 208 Nutritional Interventions Designed to Achieve Outcomes Other Than Obesity Prevention������������������������������������������������������ 214 Evidence-Based Recommendations�������������������������������������������������������� 219 What’s Next?�������������������������������������������������������������������������������������������� 220 References������������������������������������������������������������������������������������������������ 220 17 Encouraging Your Child to Be Physically Active���������������������������������� 225 Introduction���������������������������������������������������������������������������������������������� 226 Why Is Physical Activity Important? �������������������������������������������������� 226 Changes in Physical Activity with Age������������������������������������������������ 227 Geographic Variations and Temporal Trends �������������������������������������� 227 **Detailed Assessment���������������������������������������������������������������������������� 231 What Interventions Increase Children’s Physical Activity?���������������� 231 Will Exercise Prevent Your Child from Getting Fat?�������������������������� 233 Will Exercise Prevent Your Child from Developing High Blood Pressure, Heart Disease, or Diabetes? ������������������������ 235 Will Exercise Strengthen Your Child’s Bones?������������������������������������ 236 Does Exercise Make Your Child Smarter?������������������������������������������ 238 Does Exercise Improve Your Child’s Mental Health? ������������������������ 241 Summary���������������������������������������������������������������������������������������������� 243 Evidence-Based Recommendations�������������������������������������������������������� 244 References������������������������������������������������������������������������������������������������ 244 Reference Tools������������������������������������������������������������������������������������������������ 251 Index������������������������������������������������������������������������������������������������������������������ 255
About the Author
Michael S. Kramer completed most of his early schooling in Miami, Florida. He left Miami to pursue his undergraduate studies at the University of Chicago, then moved to Yale, where he completed medical school, a residency in pediatrics, and a research fellowship in clinical epidemiology. Following his education and professional training, he moved north to accept a faculty position at the McGill University Faculty of Medicine in Montreal, Canada, where he spent his entire career of 42 years and is now Professor Emeritus. He practiced clinical pediatrics for nearly 25 years, but most of his career has been devoted to research and teaching. Dr Kramer has published over 500 scientific articles and has won numerous national and international awards for his research. He has served as a member of expert committees of the World Health Organization (WHO), the U.S. Institute of Medicine, and the Council of Canadian Academies. He helped establish the Canadian Perinatal Surveillance System in 1995 and from 2003 to 2011 was Scientific Director of the Institute of Human Development, Child and Youth Health at the Canadian Institutes of Health Research. In 2011, he was elected to Fellowship in the Royal Society of Canada. Dr Kramer’s systematic review of the scientific evidence on the optimal duration of exclusive breastfeeding led directly to new infant feeding recommendations by WHO in 2001. His research on preterm birth helped draw attention to the role of labor induction and elective cesarean delivery as drivers of the rise in preterm birth from the 1980s to the early 2000s. That research contributed to obstetric guidelines to restrict provider-initiated early delivery, which have helped reverse that trend. Dr Kramer was recently cited as among the most impactful 0.01% of the world’s researchers across all scientific fields. Dr Kramer is married and has three children and six grandchildren. He plays violin and is an avid chamber musician. He also enjoys a variety of outdoor activities, including cycling, hiking, tennis, and skiing.
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Part I
Science and Parenting
Chapter 1
Does a “Good” Parent Need Science?
The most costly of all follies is to believe passionately in the palpably not true. It is the chief occupation of mankind. —H. L. Mencken
What Is Science? Defining science is an unusual way to start a book on parenting. But for this book, it is necessary. Before explaining what science is, I will start by discussing what it is not. Science is not technology. Yes, developing new technologies requires scientific training and knowledge. Conversely, many scientific advances benefit from, and may even require, technologic innovation. But technology is a tool that enables good science—not an end in itself, but a means to an end. The Large Hadron Collider (the giant nuclear accelerator located near Geneva, Switzerland) creates high-speed collisions of subatomic particles. But it is scientific hypotheses that lead to the design of specific experiments using the collider, and analysis of the data from those experiments, that lead to new knowledge about the fundamentals of matter. If you ask school-age children or most adults without formal scientific education to define science, they are likely to mention white coats, laboratory glassware, or high-tech machines. They rarely invoke the testing of hypotheses through carefully designed and conducted experiments or other studies. If science is not technology, neither is it unquestioned and untested belief in the truth of a proposition. So-called “natural” remedies are derived from natural sources and are therefore believed to be safe. Because of their long history, popularity, and apparent safety, natural remedies can be sold in pharmacies and grocery stores at any price the market will bear. But you are probably unaware that the companies manufacturing natural remedies are not required to demonstrate that they are effective, that is, that they actually work. People who buy these products do so out of
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 M. S. Kramer, Beyond Parenting Advice, https://doi.org/10.1007/978-3-030-74765-7_1
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faith: the belief that the products are effective. But because the manufacturers are not legally required to demonstrate efficacy, they don’t even try. They have nothing to gain from science and everything to lose. In contrast, drugs and vaccines cannot be legally marketed in most countries unless they have been approved by national health agencies on the basis of rigorous scientific studies that demonstrate both safety and effectiveness. These rigorous studies are called randomized controlled trials, or RCTs, and I will have much more to say about them later in this chapter. National health agencies do allow the sale of some drugs without evidence of efficacy from RCTs. Such drugs can be purchased “over the counter” without a prescription and were “grandfathered” in after long periods of prior use without major safety concerns. Cold medicines are an example of such drugs. If belief is antithetical to science, so too are anecdote and myth. Some people are unshakably convinced that their colds are always caused by exposure to cold air. Every time they come down with a sneeze and cough, they reflect back on the previous few days (or hours) and recall, “Oh, yeah, I went out on Monday when my hair was still wet” or “My office was freezing cold yesterday.” The same reasoning is applied to prevention (“I haven’t had a single cold since I started taking vitamin C tablets”) and successful recovery (“Every time I have a bad cold, my doctor prescribes antibiotics, and my cold gets better within a few days”). All of these examples demonstrate a very strong cognitive bias: “post hoc ergo propter hoc” (after this, therefore because of this), also known as the post hoc fallacy. But just as the rooster’s morning crow doesn’t cause the sun to rise, a correct temporal sequence (or, more likely, biased recollection) of events is weak evidence of causality. For example, any treatment taken for a cold will appear to be beneficial when it is taken at the peak of symptoms, since down is the only direction possible after a peak! Anecdotes tend to become reinforced by similar episodes that recur, or are selectively remembered, another type of cognitive bias called confirmation bias. Eventually, these reinforced beliefs become established as “folk wisdom.” What about the role of serendipity, a beneficial chance occurrence? Serendipity has enjoyed a rich history in science. But as Louis Pasteur famously said, chance favors the prepared mind. One often-cited medical example of serendipity is Alexander Fleming’s discovery of the antibacterial properties of Penicillium, a common bread mold that had contaminated one of Fleming’s bacteria-containing culture dishes that he had mistakenly left open. Fleming noticed a clear halo (where bacterial growth had been inhibited) surrounding the mold. The serendipitous discovery of penicillin, which is produced by the mold, ushered in the modern era of antibiotic treatment of infections. But observations like Fleming’s are not in themselves scientific. They generate hypotheses when, in Pasteur’s words, the mind is suitably prepared. Those hypotheses then lead to experiments and other studies to test the hypotheses— that is, science. When scientific tests convincingly support a hypothesis, it is said to be confirmed (“proven”).
Scientific Inference
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Scientific Inference Not all scientific inferences are cause-and-effect. Some studies have a predictive purpose, such as quantifying the probability of having a fetus affected by Down’s syndrome (a birth defect also called trisomy 21, because of a third copy of the 21st chromosome), based on measurements of various hormones and proteins in the blood during the second trimester of pregnancy. The number of study women, the methods used to recruit them, and their age and other factors will affect the accuracy of the prediction. But no cause-and-effect relationship is inferred. The hormones and proteins measured are not causes of Down’s syndrome, but rather, biological markers that help predict its occurrence and thereby help the clinician decide whether or not to recommend a more expensive test based on fetal DNA in the mother’s blood or a riskier test like amniocentesis (obtaining and analyzing a sample of amniotic fluid to examine the fetus’s chromosomes). Other scientific inquiries have a descriptive goal. Some population health studies, for example, describe geographic differences or temporal trends in occurrence of health events. Is preterm birth more common in certain states or provinces than in others? Has preterm birth in the country overall risen or fallen over time? No causeand-effect relationships are inferred from such descriptive studies, but they may lead to new causal hypotheses about why the observed geographic or temporal differences have occurred. Those hypotheses can then be tested in subsequent studies. Nonetheless, most scientific questions of interest to health (and thus to parenting) involve causes and consequences. Does spending too much time in front of a TV or computer screen cause obesity? Will vaccination prevent infection with the Hypothesized Directon Outcome (health state)
Exposure (hypothesized cause) Reverse Causality
Confounding Factor
Fig. 1.1 The essentials of causal inference. The study exposure is the hypothesized cause of the outcome, and the outcome is the health state on which an effect of exposure is hypothesized. Arrows point from causes to effects. The direction of an arrow also denotes temporal sequence; the tail occurs earlier in time than the head. Green arrows denote known or hypothesized causal directions, while the red arrow from outcome to exposure denotes reverse causality: the study outcome precedes and causes the exposure. A confounding factor is an underlying (antecedent) cause of both the exposure and outcome, and biases the apparent effect of exposure on outcome. It needs to be adjusted (“controlled”) for to remove the bias.
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microbe contained in the vaccine? Will ignoring your baby’s nighttime crying help her sleep through the night? As shown in Fig. 1.1, such questions have two essential ingredients: a hypothesized cause and a hypothesized effect. In health research, we call these the exposure and outcome, respectively. The hypothesis is that the exposure causes a change in the outcome. The process of causal inference is thus: formulate a hypothesis about an exposure and its effect on outcome, design a study to test that hypothesis, analyze and interpret the data that result from the study, and infer the validity of—that is, confirm or refute—the hypothesis.
Experiments vs Observational Studies It is important to distinguish two broad types of studies bearing on human health. The first type is called an experiment. An experiment means that the researcher actively intervenes to change the exposure and then observes the outcome in the study participants. In health research, the intervention is often a treatment intended to improve the study participant’s health, either by preventing an illness or lessening its impact— sometimes even curing it. The outcome is the health state: an illness or some measure of discomfort or disability due to the illness. A controlled experiment is a study in which two treatments are compared, or an active treatment is compared to an inactive placebo. The “control” part is key to the comparison. It provides another group of participants in whom the outcome (disease or no disease, average blood pressure, cure or no cure) can be compared to the outcome observed in the active treatment group. The controlled experiment is analogous to a laboratory study in experimental animals. One group of animals receives the active treatment, the other group receives an inactive placebo or another active treatment. Two main differences distinguish animal and human experiments: a scientific one and an ethical one. The scientific difference is that the animals who receive both treatments are usually genetically identical mice, rats, fruit flies, etc. Humans, thankfully, are not genetically identical, unless they are monozygotic (from a single fertilized egg) twins, triplets, etc. The question then becomes: How can a researcher ensure that the two groups of human participants receiving the two different treatments are identical in all respects other than receipt of the active vs the control treatment? The answer is randomization. Letting the flip of a coin or a computer-generated random sequence of numbers determine which participants receive which treatment does not guarantee that each participant is equivalent to every other participant in the two study groups. Instead, it guarantees exchangeability. Exchangeability means that the two groups are virtually identical on average and would have been equally similar had those receiving the active and control treatments been switched—in other words, had they received the opposite treatment. This type of human experiment is called a randomized controlled trial, or RCT. As mentioned earlier in this chapter, the RCT design is required for licensing new drugs. The RCT is the “gold standard” for making causal scientific inferences, not only in drug studies but in all human health research.
Experiments Versus Observational Studies
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The ethical difference between human experiments (RCTs) and animal experiments goes beyond the legal and moral necessity to obtain human participants’ informed consent. That necessity applies to all human studies, not just RCTs. But it is unethical to administer interventions that are known or suspected to be harmful to human beings, even if they consent to those interventions. We cannot randomize children to be exposed to lead vs a placebo or to physical punishment vs “time out” approaches to discipline. Instead, studies of the effects of hypothesized harmful exposures must be nonexperimental by design. We call these observational studies. Of course, RCTs also require observations; all participants must be observed to see if and when then they develop the outcome hypothesized to be caused or prevented by the active intervention. But in observational studies, the researcher does not intervene. He or she merely observes both the exposure (treatment) and the outcome and then compares the outcomes in groups of exposed and unexposed participants. Observational studies are also used to investigate exposures that are not known to be harmful, including common health behaviors and treatments chosen by the participants or their caregivers. The key feature of observational studies that distinguishes them from RCTs is the lack of exchangeability of exposed and unexposed participants that randomized treatment allocation provides. Table 1.1 compares and contrasts the main features of experimental and observational studies. As shown in Fig. 1.1, the inference that exposure causes a change in outcome critically depends on knowing the temporal sequence of exposure and outcome. Whether a study is experimental or observational, it is essential that participants have not yet developed the outcome at the time they are exposed. An outcome that precedes the exposure cannot have been caused by that exposure.
Table 1.1 Comparison of experimental and observational human health studies. Experimental studies Researcher intervenes to change exposure Interventions often referred to as treatments
Observational studies No intervention by researcher Exposure is observed, not assigned, by researcher Treatment is hypothesized to prevent or ameliorate an Exposure may be hypothesized as illness harmful or beneficial, may be a treatment Two or more exposures usually Two or more treatments usually compared: compared: Experimental (new) treatment Main exposure of interest One or more control treatments Most rigorous design randomly allocates treatment to Non-exposure or control exposure participants (the randomized controlled trial, RCT) Health outcome is observed Health outcome is observed
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Bias and Precision In the context of causal inference in human health studies, bias refers to an observed association between exposure and outcome that differs systematically (that is, not merely by chance) from the true causal effect of exposure on outcome. In other words, the researcher is likely to observe an association in the absence of a true effect, fail to observe an association in spite of a true effect, or observe an association that is stronger or weaker than the true effect. I will focus on the two most important sources of bias: confounding and reverse causality. Both are illustrated in Fig. 1.1. Confounding occurs when a third factor (neither the exposure nor the outcome) biases the association between the study exposure and outcome. The bias occurs because, as shown by the arrows in Fig. 1.1, the confounding third factor is an underlying (antecedent) cause of both the exposure and the outcome. For example, let’s say we knew nothing about the fact that cigarette smoking causes lung cancer. A clever researcher carries out an observational study of 100 cases of lung cancer and 100 controls without lung cancer; this is called a case-control study. The researcher carefully interviews and examines the 100 cases and 100 controls. Of the 100 cases, 30 are found to have yellow fingers on their dominant hand, whereas only 3 of the 100 controls have this finding. It would be incorrect to infer that yellow fingers cause lung cancer, because (as we now know) both the yellow fingers and the lung cancer are caused by smoking cigarettes. This bias can be reduced or eliminated by measuring and adjusting for the confounding factor through one of several statistical techniques. For example, if we analyze smokers and non-smokers separately, we will find none of the non-smoking cases or controls to have yellow fingers, but a similarly high proportion of smokers with yellow fingers both among cases and controls. The second important source of bias is reverse causality. It is illustrated by the red arrow in Fig. 1.1. This bias occurs when the outcome actually precedes and causes the exposure, rather than the reverse. It is particularly likely to occur in what are called cross-sectional studies, because exposure and outcome are ascertained at the same moment (cross-section) of time. For example, many of the studies investigating whether a large number of hours per day spent in front of a television or computer screen causes obesity are based on a cross-sectional design in which children are weighed and measured and parents are interviewed about how many hours per day the child spends watching television or using a computer. If those measurements and interviews occur around the same time, we have no way of knowing if a positive association reflects the causal effect of prolonged screen time on obesity or the causal effect of obesity on increasing screen time. Either direction is biologically plausible. The only way to be sure of inferring the correct direction is to design a longitudinal (prospective) study in which the hypothesized cause, prolonged screen time, is measured at a baseline time when all eligible study children have a normal body weight. The children are then followed up over time, and the proportion of new cases of obesity is compared in children with and without prolonged screen time at baseline.
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Confounding and reverse causality biases are much more likely in observational studies than in randomized trials (RCTs). Because “association does not prove causation,” it is sometimes claimed that causal inference requires a randomized trial. But bias can occur even in randomized trials. For example, confounding can occur if the treatment received is not well concealed from participants or care givers (we say they are not “blinded”) and leads to other co-interventions that affect the trial outcome. On the other hand, well-designed observational studies that consistently show strong associations with a dose-response relation (for example, higher risks of the outcome in participants with higher levels of exposure), as well as confirmation in repeated studies in different settings, often provide sufficient evidence of causation to take action. That cigarette smoking causes lung cancer can no longer be debated, despite the efforts of tobacco companies to undermine the “merely observational” evidence base. The reduced lung cancer risk in ex-smokers, the fall in lung cancer incidence in countries that have succeeded in reducing their smoking rates, and the rise in incidence in other countries with increased smoking provide strong evidence of causality despite the “observational” design of the studies demonstrating the association. Similar arguments can be made for prone sleeping position as a cause of the sudden infant death syndrome, or SIDS. Precision is different from bias. Like bias, insufficient precision can lead to an error in the estimate of an exposure-outcome association, whether that estimate comes from an observational study or an RCT. Unlike bias, however, precision is the degree of uncertainty about the magnitude of association due to chance variation. Imprecision, or low precision, leads to an estimate that is not systematically too high or too low, but one that shows a wide range of statistical uncertainty around the observed estimate. It is usually due to a small sample size and often prevents detection of a true association or effect. The observed association or effect is called statistically non-significant. In other words, it may be entirely attributable to chance. For example, if our abovementioned study of lung cancer and yellow fingers had included only 10 cases and 10 controls, we might have observed 3 cases and no controls with yellow fingers. That would be a statistically non-significant result, because the sample size of only 20 total participants might well yield a difference of this magnitude (3 out of 10 vs 0 out of 10) solely by chance even if yellow fingers had no association with lung cancer. This “false-negative” finding has nothing to do with confounding by cigarette smoking. It is merely a consequence of an insufficient sample size, that is, imprecision.
Does a “Good” Parent Need Science? Science is no substitute for love and affection. It is not even a strong competitor. Love and affection are emotions, not decisions. You do not decide to love your child or to show her affection. In contrast, parental decision-making is usually conscious and carefully considered, especially for major decisions. I am not referring here to
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deciding whether to serve broccoli or carrots at your baby’s supper this evening. But careful reflection is required when you decide whether to abstain from alcohol during pregnancy; whether to vaccinate your child, and which vaccines you should or should not obtain; whether to breastfeed or formula-feed your newborn baby; whether to “train” your infant or toddler to sleep through the night; how much, if any, television and screen time you should allow your child; how to control your child’s misbehavior; and how strict to be in establishing and enforcing your child’s bedtime. Decisions are choices. Making an appropriate choice requires you to list the realistic alternatives. You must then weigh the evidence among those alternatives, which can require quantifying (or at least ranking) their respective benefits, risks, efforts, and costs. You then must attach your own values to those benefits, risks, and costs. Finally, you should choose the alternative that maximizes the overall value of your choice for your child, for your family, and for society. Two different parents, even within the same family, may not arrive at the same decision. Despite receiving the same information from me, my daughter Elise and daughter-in-law Sarah made opposite decisions about whether to drink alcohol during their pregnancies. Although the health benefits and risks are often the same for most children, some parents tend to be more risk-averse than others. And you may not be willing to spend the effort or money required by some of the alternatives. Nor is conformity with “expert” recommendations an ideal recipe for making your parenting decisions. Different experts (or expert groups) may disagree. Many expert recommendations are based on minimizing risks for all children, even when the risks are already extremely low and even when considerable parental effort is required to reduce them further. Social interaction among fellow parents can lead to a “herd effect” by which parents in groups defined by geographic, cultural, religious, or socioeconomic commonalities encourage similar or even identical decisions by parents in the group. Instead of following expert advice or your group’s norm, you may want to know more about the scientific basis underlying that advice and those norms. If you seek the evidence (or lack thereof) for risk and harm of your parenting choices, this book is for you. Key Points • A key aspect of science is the rigorous testing of cause-and-effect hypotheses. • The randomized controlled trial (RCT) is the human analog of an animal experiment and is the scientific “gold standard” for testing causal hypotheses in human health. • Biases are systematic errors that can lead to erroneous causal inferences, especially in observational (non-experimental) studies.
Chapter 2
Summing Up: Synthesizing the Scientific Evidence
Beware of false knowledge; it is more dangerous than ignorance. —George Bernard Shaw
Why Synthesize the Evidence? If you are reading this book, you want access to the best scientific evidence before making decisions concerning your pregnancy and your child’s health. In today’s world, such access usually means online access. Most people start with an Internet search, selecting one or a few summaries from sources they believe to be reliable and unbiased or that seem useful. But a simple Google search won’t cut it, because you and other people without epidemiologic or other training in research methodology are not usually able to sift through the mountain of “hits” and separate the grain from the chaff. The most recent study also doesn’t cut it—it almost never replaces all those that precede it. It is true that knowledge increases over time, but the process is not linear. Sometimes it is two steps forward, one step backward. Even for doctors and other health providers, keeping up with the best evidence is tough. They often rely on reviews published in their specialty’s journals; some even subscribe to a regular (monthly, for example) review service that summarizes topics in the diagnosis and treatment of conditions relevant to their practice. Similarly, governments, insurance companies, and other organizations responsible for health systems or policy also depend on up-to-date scientific evidence. They often seek reviews in scientific journals and publications by professional societies and government agencies. Unfortunately, most reviews are narrative descriptions. That is, they tell a story in a way that is digestible for the intended audience. Their readability is a strong point, but they are seriously flawed in one important respect: they are shaped by the reviewer’s choices. They are therefore almost always selective, incomplete, and
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unverifiable. In other words, they tend to be biased. The reviewer may be biased by her prior opinion, or she may make an honest appraisal rooted in her past experience, augmented by a recent literature search. But the reader has no way of knowing how she selected the studies cited in her review. Selective citation of published studies can lead to serious bias in reviewing scientific evidence. This is often referred to as “cherry picking,” a colloquial expression for bias due to selective citation of studies when reviewing the evidence. You may well ask, “But isn’t the reviewer an expert in the field? If so, why shouldn’t I trust her?” The answer is simple. Two expert reviewers can and often do disagree with each other. Both of their reviews are readily available, either from Professor Google or via a library search. What are you, as a parent seeking a review of the published evidence, supposed to do when faced with two (or five!) conflicting expert reviews? That is the problem. A personal anecdote will illustrate the problem. In 1995, I was meeting with potential Belarusian obstetrician and pediatrician collaborators to discuss a large RCT we were planning to conduct in their country, Belarus. The RCT’s goal was to assess the impact of a breastfeeding promotion intervention on infant feeding practices and the health of the offspring. (I will have more to say about this study in my chapter on infant feeding.) At that 1995 meeting, I was discussing the strengths of the RCT design with my collaborators, reviewing many of the arguments I made in Chap. 1 of this book. I asked them how they decide between two different treatment options for their patients. “We ask an expert,” they replied. “But,” I countered, “what if you ask two different experts, and the two give opposite advice?” “Then we’d ask a third expert,” they responded, “a bigger expert.” That response got a few assenting nods, but also a good laugh from the attendees. The episode underlines the problem of reliance on expert opinion. The truth is, conflicting views or interpretations of the evidence are the rule, not the exception. Expert judgments are not mere mechanical, arithmetical manipulations. Rather, they must consider the quality of the studies: their potential for bias, their size, and their representativeness. Quality assessments are both time-consuming and subjective. What is the alternative? What should you do when faced with conflicting expert opinion? Or even in the absence of conflict, should you follow the crowd, that is, the shared opinion of your friends, family, church, or yoga class (what I referred to as the herd effect in Chap. 1)? My suggestion is to distrust expert opinion, no matter how “big” the expert, and also to distrust your “herd.” The preferred alternative is called a systematic review, which I describe in the following section.
Systematic Review Unlike a conventional review, a systematic review is a research study in its own right. In fact, it can require greater effort and time than a new, independent study. Like an individual research study, it should attempt to test a specific scientific
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hypothesis: often, a causal hypothesis that a specific treatment or other exposure affects one or more subsequent health outcomes. For example, we might want to review the published evidence comparing the effects on subsequent aggressive child behavior of physical punishment, “banishment” to the bedroom, or removal of privileges in school-age children who exhibit some undesirable behavior. Systematic reviews are also useful for descriptive and predictive studies. Like an individual research study, a systematic review benefits from a formal protocol written beforehand. The protocol states the objective(s) of the review: usually, the causal question to be addressed. The protocol also details the bibliometric methods (which electronic databases, keywords, and logic) to be used in searching the literature for published studies and the criteria by which studies will be included in or excluded from the review. It should also indicate how the reviewer(s) will assess the quality and validity of each study meeting the inclusion criteria. Finally, the protocol should describe the methods to be used to synthesize the evidence from the collected studies. These include both qualitative synthesis (a descriptive summary of the characteristics, strengths, and weaknesses of the assembled studies) and, if justified, a quantitative pooling of data and statistical analysis across studies (meta-analysis). Many of the published systematic reviews I cite are limited to a narrative summary of the studies reviewed, summarizing their designs, geographic settings, and main results in text and tables, perhaps also commenting on their individual strengths and weaknesses. Others provide that information but also include a meta-analysis. Some narrative systematic reviews omit meta-analysis because they judge the characteristics or results of the studies to be too heterogeneous to pool, but most do not state the reasons. A systematic review takes far more time to complete than a conventional review and may require research funding (a grant). It also requires expertise in research methods, statistical analysis, and the substantive area under review. Although a single author may have expertise in all of these areas, a collaborative team is often necessary. Moreover, collaboration is helpful to enhance the validity of the many judgments needed on study eligibility and quality, and of the data extracted for meta-analysis. Table 2.1 compares and contrasts systematic and conventional reviews.
Reviewing the Evidence on Parenting In the remainder of this book, I will apply the principles laid out in the first two chapters. The areas covered will be divided into three main sections, one each on pregnancy, infancy and toddlerhood (the first 2–3 years of life), and childhood and adolescence. Each of those sections contains several chapters, each covering an important topic. I do not review every topic of interest or relevance to pregnant women and new parents. Those concerning common infections, injuries, and other illnesses are not
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Table 2.1 Systematic vs conventional reviews of published scientific evidence. Systematic review Addresses a specific scientific hypothesis Benefits from a formal protocol that specifies objectives and methods: Inclusion/exclusion criteria Bibliometric methods Data extraction and analysis Assessment of study quality Meta-analysis, if justified Very time-consuming, may require funding Requires expertise in research methods, statistics, and substantive area (collaboration) Less susceptible to reviewer bias
Conventional review Often topic-driven, not hypothesis-driven Narrative format, no prior protocol, no formal methods, no meta-analysis
Requires skill and time, usually unfunded Requires expertise in substantive area Often biased by selective citation (“cherry-picking”)
particularly controversial and are well covered by existing books and online resources. Instead, I focus on topics characterized by the high frequency of their occurrence, the need for parental decisions, and the plentiful but confusing advice about what you should decide. These are topics for which rigorous and systematic review of the published evidence should be most helpful in providing you with a complete and unbiased source of the science underlying the decisions you will have to make. As mentioned in the Preface to this book, your doctor or other health provider is unlikely to be familiar with this evidence and may be surprised to learn how you came to your decisions! In line with the arguments made in this chapter, I will heavily rely on systematic reviews. These will not be my systematic reviews. Since you have made it this far, you will appreciate that even a single original systematic review relevant to any one of the 15 topic areas that comprise the remainder of this book is a major undertaking that could require as much of my time and effort as this entire book. The time required to carry out an original systematic review of all topics in this book would far exceed my remaining life expectancy. Moreover, such an undertaking would also ignore the thought and work that other researchers have put into publishing their systematic reviews. You may now believe that the conclusions of a systematic review are an objective, almost arithmetic, summary of the evidence. That would be nice, but systematic reviews unfortunately cannot avoid subjectivity. Subjective choices are made in searching the published literature, deciding the eligibility criteria for studies to be included, which studies meet those criteria, the quality of the included studies, and whether or not to pool (meta-analyze) the results across studies. It is not rare for two systematic reviews on the same topic to reach different conclusions. But at least, it is usually far easier to understand why they disagree than it is with conventional reviews. I will therefore base my assessment of the evidence on systematic reviews wherever possible. I will summarize that evidence and, where justified, offer some
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recommendations that should affect your decision choices. For topics on which I am unable to find systematic reviews, I will not conduct my own. Instead, I will mention their absence and summarize the results of what I believe to be the best individual studies on that topic, as well as the major outstanding issues requiring resolution. I will also comment on the overall strengths and weaknesses of published studies in the topic area and on how to fill the major evidence gaps. Most published studies are conducted by researchers living and working in high- income, Western settings, although some have examined within-country ethnic or socioeconomic differences in associations between exposures/treatments and outcomes. High-quality research from some Asian countries has also become increasingly common in recent years. But the evidence base remains weak for many areas of the world, especially the Middle East and sub-Saharan Africa. I will try to identify ethnocultural gaps in the evidence base and speculate about why the published literature might, or might not, apply to pregnant women and parents in different geographic areas or ethnocultural groups. Finally, the evidence I review should influence, and in many cases already has influenced, recommendations for clinical practice, health policy, and education. Those recommendations, when appropriately based on systematic reviews of the scientific evidence, attempt to yield the greatest benefit and least harm and cost, on average, for the general population. But you are probably less interested in the best decision for the general population than what is best for your child. Your decision should consider how you and your family value the benefits, risks, effort, and cost associated with each choice. In this book, I attempt to quantify the estimated benefits and risks. Those estimates are statistical probabilities of good and bad outcomes, respectively. But weighing the estimates, and deciding whether the effort and cost of maximizing the benefits and minimizing the risks are worth expending, depend on your values—not mine and not even society’s. Key Points • Conventional reviews of published evidence are highly susceptible to bias due to selective citation (“cherry picking”). • In contrast, systematic reviews use rigorous methods to find all relevant studies, evaluate their strengths and weaknesses, and (if justified) pool their results. • Ideally, systematic reviews of the scientific evidence should inform your decisions concerning your baby and child, especially where that evidence is complex and conflicting. • The benefits and risks associated with alternative decision choices can often be estimated from systematic reviews, but your values of those benefits and risks, as well as the effort and costs required to achieve them, are likely to vary from those of other parents.
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How to Read the Rest of This Book As mentioned in the Preface, you can read this book by selecting chapters of particular interest to you. Now that you’ve read the first two chapters and understand the basic scientific and epidemiologic concepts discussed therein, you can skip around and limit your reading to those chapters or parts of chapters that are important to you. I have provided a Reference Tools guide with glossary, so that you can refer back as needed to the terms and concepts that are unfamiliar to you. Readers of any of the chapters in the pregnancy section should first read the Preface to the Pregnancy Section, because that Preface lists and explains the pregnancy outcomes shared by all of the pregnancy chapters. Each of the remaining chapters is organized in a similar fashion. It begins with a Pre-Reading Quiz Question to whet your appetite for reading further. The correct answers to these questions are likely to surprise you; they are provided about halfway through the chapter, just after the Key Points and before the Detailed Assessment. After the Quiz, the chapter proceeds with an Introduction: why the topic is important for you, your child, and for public health, and the list of exposures and (for the childhood sections of the book) outcomes that I will review. After the Introduction, I summarize the conclusions (Key Points) that emerge from the pertinent systematic reviews, followed by the correct answer to the Quiz Question that kicked off the chapter. The final and largest section of each topic chapter is the Detailed Assessment, which discusses research design issues relevant to the topic, assesses the quality of the evidence base, and provides the detailed results and published references of the systematic reviews and individual studies that contribute to the Key Points. Reading the Detailed Assessment is not essential to get the gist of the chapter but is included for those of you who want to delve more deeply and/or consult the cited references. It is marked by two asterisks (**) to make it easy to skip. If you do read this section, you may want to re-read bits of the first two chapters or to refresh your understanding of key terms and concepts. Readers who do not read the Detailed Assessment should nonetheless read the Evidence-Based Recommendations that conclude each chapter.
Part II
Pregnancy
Preface Unlike the many age- and topic-specific outcomes that are important for infants, toddlers, older children, and adolescents, the health outcomes relevant to pregnancy are the same, regardless of which exposure is being considered. Each of the chapters in the pregnancy section of the book is organized around a specific exposure or group of exposures like maternal weight, physical activity, drugs, medications, and vaccines. The pregnancy outcomes that are potentially affected by these exposures are similar for each exposure. To avoid listing and explaining the same outcomes in each chapter, I will do so in this Preface. Here is the list of outcomes: • • • • • • • •
Infertility Miscarriage (fetal death before 20 completed weeks of pregnancy) Stillbirth (fetal death at >20 weeks of pregnancy) Congenital anomalies (birth defects) Gestational diabetes mellitus (GDM) Gestational hypertension (high blood pressure) and pre-eclampsia Preterm birth Fetal growth –– Small for gestational age (SGA) –– Large for gestational age (LGA)
• Cesarean delivery Preterm birth and fetal growth require some explanation for those unfamiliar with these concepts. The World Health Organization (WHO) defines preterm birth (commonly referred to as prematurity by the general public) as a gestational age at birth below 37 completed weeks, or 259 days. Babies born more than 3 weeks earlier than the full term of 40 weeks (280 days) are at increased risk of a number of adverse short- and long-term outcomes: neonatal death (death in the first month of
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life), post-neonatal infant death (death between 1 month and 1 year), respiratory distress syndrome caused by immature lungs, intestinal problems, infection, eye problems caused by underdeveloped retinas, cerebral palsy, and less severe neurological, cognitive, and behavioral problems. But gestational age at birth can range from 20 weeks after the first day of the last menstrual period to 42 weeks or more. Even babies born at 37 or 38 weeks are at slightly higher risk of the above-listed problems than those born at 39 or more weeks. But the risks sharply increase with increasing degrees of prematurity. Babies born at below 32 weeks are considered very preterm, and those below 28 weeks extremely preterm; they are at much higher risk. In general, exposures that increase the risk of preterm birth also increase the risk of very preterm and extremely preterm births. Like gestational age, fetal growth is also measured on a continuous scale. This scale is called birth weight for gestational age, which is often divided into three categories: small for gestational age, or SGA (usually defined as a birth weight in the bottom 10% of an appropriate population reference); appropriate for gestational age, or AGA (ranging from the 10th to the 90th percentile of the same reference); and large for gestational age, or LGA (in the top 10% of the reference). SGA infants are at increased risk for some newborn problems like low blood sugar or infection and minor long-term deficits in height, weight, and cognition. They are also at slightly higher risk of dying in the first year of life—but at much lower risk than infants born preterm. LGA also carries some risks; the larger size of LGA infants can lead to difficulties at delivery, including a cesarean, and also a higher risk of obesity as children and adults. As with preterm birth, the risks associated with SGA and LGA depend on degree. SGA babies with birth weights in the lowest 1% are at much higher risk than those born between the lowest 1% and lowest 10%. The same is true for LGA babies in the highest 1% vs those between the highest 1% and the highest 10%, although the outcomes in LGA babies are generally less severe than those in SGA babies. And as with preterm birth, factors that increase the risk of SGA or LGA will generally also increase the risk of extreme SGA or LGA. When I arrived at WHO for my sabbatical leave in 1984, I was asked to review what was known about the causes of low birth weight (LBW). WHO defines low birth weight as a weight of a newborn infant below 2500 g (around 5.5 pounds). But birth weight is determined by two very different factors: (1) the gestational age at birth (how long the pregnancy lasts, usually measured in completed weeks) and (2) fetal growth (how fast the fetus grows, usually measured in birth weight for gestational age). A newborn baby can therefore have LBW because she is born too soon (preterm birth), or because she has grown too slowly (is small for gestational age, SGA), or both. This is obviously not rocket science, but it took me quite a while to get my head around the published literature I was asked to systematically review. In 1984, most authors continued to report on LBW, rather than separating the outcomes into preterm birth and SGA. In some low-and middle-income countries, gestational age was either not reported or was felt to be unreliably reported. But for those studies that did report separately on preterm birth and SGA, it was clear that the effects of maternal undernutrition, short stature, cigarette smoking, and several other
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exposures were far weaker on preterm birth than on SGA. Yet it was also very clear that the strong association between LBW and infant mortality (death of a live-born baby before his or her first birthday) was mostly due to the high death rate of preterm babies, owing to the immaturity of their lungs, brains, and immune systems— not term babies (at least 37 completed weeks) born SGA. I have provided this detailed personal background for several reasons. First, to illustrate that old ideas die hard. Despite my (and many others’) work in this field for the last 35 years, LBW continues to be reported, both in population health statistics and as an outcome in research studies. Yet no one, to my knowledge, has demonstrated its utility for public health policy, clinical care, or decision making by pregnant women, their families, or the societies in which they live. This is the reason you will not see the term “low birth weight” (or its LBW abbreviation) again in this book.
Chapter 3
How Much Should You Weigh? Body Weight Before and During Pregnancy
Thou seest I have more flesh than another man, and therefore more frailty. —William Shakespeare, Henry IV, Part 1
Lea Kron
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Pre-Reading Quiz Question Which of the following statements is true? A. How much weight you gain during your pregnancy is more important for the health of your baby than how much you weigh before you get pregnant. B. Being underweight (too thin) before pregnancy is more harmful to your baby than being overweight. C. Being overweight before pregnancy substantially increases your risks of miscarriage, birth defects of the heart and brain, and stillbirth. D. All of the above. E. None of the above.
Introduction When I arrived at the World Health Organization (WHO) in 1984 and began my systematic review of the causes of preterm birth and restricted fetal growth, WHO’s major concern was the effect of maternal undernutrition in developing countries (now referred to as low- and middle-income countries, or LMICs). Maternal undernutrition comprises several separate, albeit related, issues. Chronic (longstanding) early-life undernutrition leads to stunting, that is, short stature. Some “catch-up” growth in height can occur later in childhood if nutrition improves and gastrointestinal infection (diarrhea) becomes less frequent and less severe. Yet, many stunted children remain short, and the final adult height is lower than would have been the case without the early stunting. In addition to stunted height, undernourished young children also have low weight. Unlike the permanent deficit in height, low weight can be reversed at older ages if better nutrition becomes available. In poor, rural settings in Asia and sub- Saharan Africa, however, many children and young adults, including young women of childbearing age, are not only short but thin. In other words, their weight is low even for their reduced height.
Pre-Pregnancy Body Mass Index (BMI) Weight for height is usually measured using the body mass index (BMI), which is the weight divided by the height squared, expressed in metric units of kg/m2. Although the BMI does not distinguish fat from muscle, it is easy to measure and is highly correlated with body fat. In most Western populations, the following categories of BMI ranges are often used: underweight (