During her pregnancy, Emily Oster didn't appreciate her doctor's habit of issuing blanket rules: Don't gain more than 35 pounds. No need to discuss amniocentesis — you're not 35. No eating in the delivery room.
An edict to limit coffee to two cups a day particularly irked Dr. Oster, a health economist at the University of Chicago whose workday was powered by a "pretty steady caffeine drip."
Her ob-gyn issued decrees without explanation, much as a parent says "no" and expects compliance. But Dr. Oster, a Ph.D. trained in statistics who is not a medical doctor, could not imagine making an informed decision without some data. Her new book is the result of weekends sifting through PubMed and other scientific databases; reading a textbook, Steven Gabbe's "Obstetrics"; and chewing over issues with friends in the field to figure out which pregnancy rules were supported by convincing evidence.
"Expecting Better" will be a revelation for curious mothers-to-be whose doctors fail to lay out the pros and cons of that morning latte, let alone discuss real science. And it makes for valuable homework before those harried ob-gyn appointments, even for lucky patients whose doctors are able to talk about the rationale behind their advice.
But her confrontational approach may well alienate some readers, not to mention doctors, and some experts are questioning the accuracy of her advice on alcohol.
Some of myths she attempts to explode were already on the ropes. It's widely known that bed rest — recommended to supposedly prevent preterm labor — is supported by little evidence and could cause harm. And Dr. Oster, 33, notes that "fertility declines with age, but not as fast as you might expect." But as luck would have it, she got scooped by an article in The Atlantic that argued — with statistics — that a decline in fertility in a woman's 30s has been oversold.
She's on fresher terrain dissecting two tests performed late in pregnancy. The nonstress test, done to assess fetal distress, depends on measurements of the heart rate and the fetus' movements. Simply clapping loudly can wake the fetus and get her moving. Good to know.
And if an ultrasound finds that amniotic fluid is too low, Dr. Oster writes, there are two possible solutions. Make sure the so-called deepest vertical pocket is being measured; alternately, drinking two liters of water before the test can raise amniotic fluid levels. That's useful advice, especially since a low reading can lead to induced labor.
Yet some of her conclusions are less well supported by medical research. After reviewing small studies showing that exercise has little impact on rates of C-sections, fetal growth or labor length, she concludes that exercise is "fine" for pregnant women but so is abstaining for nine months. The latter approach overlooks the broad health benefits of exercise, pregnant or not.
Dr. Oster's thoughts on drinking alcohol while expecting have already generated controversy. In her view, there is no good scientific evidence that light drinking negatively impacts the fetus. Pregnant women can be comfortable with "1 to 2 drinks a week in the first trimester" and one drink daily afterward, she writes.
Similar assertions have long been made, but her explanation may be unique: a woman who drinks slowly lowers the amount of alcohol and acetaldehyde, its toxic byproduct, reaching her fetus.
Most government agencies and the American College of Obstetricians and Gynecologists say that no amount of alcohol has been proved safe for the developing fetus, a position Dr. Oster calls "draconian."
Bill Dunty, a program director of the division of metabolism and health effects at the National Institute on Alcohol Abuse and Alcoholism, called her explanation "oversimplified" and said it could "potentially mislead women to think they are not exposing their fetus to alcohol."
Women vary in their ability to absorb and metabolize alcohol, according to Dr. Dunty. "It is unrealistic to believe that an individual can inherently control the amount of alcohol or its metabolites that reach her fetus by taking longer time to drink an alcoholic beverage," he said.
Dr. Oster contends that acetaldehyde is processed "by the baby's liver and doesn't get into the brain."
However, the fetal liver is not formed until at least week 20, and it doesn't become fully functional until just before birth, says Jacquelyn Bertrand, a senior scientist at the National Center on Birth Defects and Developmental Disabilities at the Centers for Disease Control and Prevention.
What's more, ethanol crosses the placenta and becomes part of the amniotic fluid, said Dr. Bertrand, who has a Ph.D. in psychology and has studied the neurodevelopment of children with prenatal alcohol exposure. Even with very slow drinking, ethanol builds up in the amniotic fluid. which bathes fetal tissue for a considerable time, she said, adding that all fetal organs, especially the brain, are very vulnerable because sometimes they are in direct contact with amniotic fluid.
Throughout "Expecting Better," Dr. Oster paints a fairly antagonistic picture of the doctor-patient relationship, castigating what she views as the restriction of women's freedom.
Dr. Jeffrey L. Ecker, the chairman of the committee on obstetrics practice for A.C.O.G., acknowledged that doctors used to take a "directive approach of 'Do this, don't do that, end of story.'" But now, he said, relationships with expectant patients have evolved into more of a "shared decision-making model."
"I wouldn't equate offering a recommendation, even a recommendation that doesn't have the strongest possible evidence, with restricting someone's freedom," Dr. Ecker said.
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