If someone told you to alter your daily behavior, the first question you’d probably ask would be “Why?” And if you were told your actions were “risky,” you'd likely wonder “How risky?” Driving, cycling, staying home—everything we do carries some risk. The usual question is, how much risk is acceptable? Yet there are a few arenas where we tolerate zero risk, demanding lifestyle changes first and asking questions later. As anyone who's flown since 9/11 knows, national security is chief on that list. And so is pregnancy. Pregnant women give up foods, beverages, and behaviors because they're told, “You can never be too careful.” Emily Oster, bless her, says, “Oh, yes you can.”
Oster, a University of Chicago economist, was prompted by the frustrations of her own pregnancy to run the numbers on the standard prohibitions. In her new book, Expecting Better: Why the Conventional Pregnancy Wisdom Is Wrong—and What You Really Need to Know, Oster aims a welcome arsenal of data at a subject usually treated with hysteria. Although the book’s tone can get oddly glib and some of the myths she debunks were never really bunked in the first place (yes, you can have sex while pregnant), on the whole, Oster's book is surprising and useful. Oster makes a persuasive case that much of what pregnant women are told today is simply wrong, and that many of those “risky” behaviors aren’t so risky after all.
You can drink coffee (a lot)
Bump, a Brooklyn maternity store, advertises itself with the slogan: “Give up wine, coffee, sushi—not fashion.” Whether or not one ever had fashion, coffee is definitely on the “not recommended” list these days. Certain doctors and the Mayo Clinic Guide to a Healthy Pregnancy recommend avoiding coffee, while others suggest drinking it only “in moderation.” But for people (like Oster) who routinely consume three to four cups per day, are there persuasive reasons to stop? Not according to some of the data. The presumed risk for coffee drinkers is a higher rate of miscarriage, but a 2008 study in the journal Epidemiology found that those who drink up to three cups per day have the same risk as light coffee drinkers and abstainers.
—“Caffeine and Miscarriage Risk,” Epidemiology 19, no. 1, by D. A. Savitz et al, January 2008
You can drink booze (a little)
We know the effects of fetal alcohol syndrome (caused by heavy drinking during pregnancy) are real. What’s harder to quantify is the effect of light drinking. The studies on light drinking (up to a drink a day) during pregnancy seem to have contradictory outcomes, but Oster sifts through the data to show that not all studies are created equal. One of her favorites, from researchers in Australia, looked at a large group of women and included long-term follow-ups on their children. Children of light drinkers turned out to have slightly higher IQs than those who abstained completely—not enough higher to be statistically significant but enough to put to bed those fears that a small glass of wine could be harming your unborn child. On the other hand, Oster dismisses a 2001 U.S. study used to justify the prohibition on light drinking because she thinks it failed to adequately account for the fact that many of the study’s drinkers were also doing cocaine while pregnant. Don’t do cocaine.
—“Prenatal Alcohol Exposure and Attention, Learning, and Intellectual Ability at 14 Years: A Prospective Longitudinal Study,” Early Human Development 83, no. 2, by F. V. O’Callaghan et al, February 2007
Prenatal tests aren't so scary
Prenatal tests are stressful. They involve imagining a whole array of potential disabilities and trying to determine what your response would be to each. On top of that, the tests themselves can carry risks, and balancing the risk of an undetected condition against the risk of a test can be a conundrum. But just how risky are invasive tests? The statistics commonly cited are that one out of every 200 amniocentesis tests and one out of every 100 CVS (chorionic villus sampling) tests result in an accidental miscarriage. That’s a pretty risky risk. But Oster reports that those stats are 30 years out of date, coming from a time when these procedures were much newer. With years of practice and new technologies, doctors have gotten better at performing the tests, and the risk rates have gone down accordingly. Using a group of recent studies (some of which show performing the tests as no riskier than not performing them), Oster comes up with an estimate that amniocentesis and CVS each have a miscarriage risk of between 1 in 600 and 1 in 800.
—“Evaluating the Rate and Risk Factors for Fetal Loss After Chorionic Villus Sampling,” Obstetrics & Gynecology 112, no. 4, by A. O. Odibo et al, October 2008
Get out of bed
As many as 20 percent of pregnant women will be on bed rest at some point during their pregnancies, so there must be some good reason for it, right? Doesn’t look that way. Oster couldn't find a single study suggesting that bed rest improves outcomes for babies. One study in particular found that bed rest neither prevents preterm birth nor increases birth weight—its supposed primary benefits. So if bed rest doesn’t help, at least it can’t hurt, right? Wrong. Bed rest’s risks range from the practical (there’s a real economic drag inherent in removing yourself from normal wage-earning activities and having to hire someone to fill in at home) to the physical (bed rest could cause serious health problems, including bone loss, muscle atrophy, and blood clots). If a treatment has only downside and no known upside (except catching up on Mad Men), it seems reasonable to assume that the treatment isn’t really a treatment at all.
—“Lack of Evidence for Prescription of Antepartum Bed Rest,” Expert Review of Obstetrics & Gynecology 6, no. 4, by J. A. Maloni, July 2011
Keep your cat, but buy gardening gloves
Most pregnancy books have a quick throwaway line about cats, warning pregnant women away from the litter box. Cats that eat raw meat can have the toxoplasmosis parasite, which is transmitted through feces, so the standard strategy is to ask your partner to change the box. Some women even go so far as to get rid of their cats during pregnancy. But is it worth finding a litter-sitter? As it turns out, no. A study of pregnant women in Europe found that cat ownership had no bearing on toxoplasmosis exposure. Cats are only capable of transmitting the disease when they are first exposed to it. If you have an outdoor cat, odds are he or she was exposed long ago and no longer poses a risk. Based on the European study, Oster recommends avoiding acquiring kittens mid-pregnancy (they’re more likely to get the disease for the first time). She also advises taking extra care in the garden because the study did find a strong association between toxoplasmosis and working with soil. Plants are apparently far riskier than Felix.
—“Sources of Toxoplasma Infection in Pregnant Women: European Multicentre Case-Control Study,” BMJ 321, no. 7254, by A. J. C. Cook et al, July 2000
Five Studies is Pacific Standard’s biweekly column that identifies and analyzes the best academic research to deliver new insights on human behavior.