Bisphenol A, phthalates, polychlorinated biphenyls, polybrominated diphenyl ethers—these barely pronounceable chemicals contaminate the bodies of nearly all American pregnant women. Worse, research suggests that most pass through the placenta and into the bloodstream of developing fetuses. But how scared should expectant parents be? Sometimes the way risks are reported makes chemicals sound more dangerous than they really are, and in any case many environmental health risks are surprisingly easy for pregnant women to avoid.
Scientists often estimate the seriousness of a chemical health risk by comparing the magnitude of harm that befalls exposed individuals with that which befalls the unexposed. This calculation typically provides a relative risk estimate—for instance, the 2013 finding that babies born to pregnant women exposed to high levels of pesticides are 30 to 50 percent more likely to develop brain tumors as children. Yet what is often left out of studies and news reports—in part because it can be difficult to estimate—is the baseline risk. Only about one in 20,000 kids is typically diagnosed with a brain tumor, so a mom highly exposed to pesticides has, at most, only a one in 13,333 chance of giving birth to a baby who goes on to develop a brain tumor. A large increase in risk, then, should not always incite a large amount of concern; conversely, a small increase in risk in a common condition could be important.
Expectant parents should not forget the old adage “the dose makes the poison,” either. Children exposed to high levels of the pesticide DDT are more likely to suffer impaired verbal learning and motor development problems, but research findings conflict on how chronic low levels of exposure—which are far more common—affect brain development. “It is often the case that the kinds of doses people get in everyday life are vastly smaller than the kinds that were studied in the original research,” says Brian Zikmund-Fisher, a decision psychologist at the University of Michigan Risk Science Center. Moreover, some chemicals pose health problems only beyond a certain threshold of exposure, whereas others might actually be more dangerous at low concentrations than at high ones.
More important, most environmental health studies conducted in people identify associations, not cause-and-effect relations. Certainly the fact that people who have high levels of BPA in their urine are more likely to be obese provides a hint that BPA may cause weight gain. Yet BPA exposure is also associated with other choices, such as processed food consumption, which can cause the numbers on the scale to creep up. Not all chemical associations are causal.
That all said, pregnant women can make smart, simple decisions to protect their unborn babies. Being a nonsmoker is a big one because cigarette smoke interferes with many aspects of development. Eating good food, and preparing it carefully, can make a big difference, too. “Eat low on the food chain, wash your fruits and vegetables before you eat them, and try to eat fresh rather than processed foods—all these things will help because they have the benefit of increasing your nutritional consumption and decreasing your chemical exposures,” says Tracey Woodruff, director of the Program on Reproductive Health and the Environment at U.C. San Francisco. These kinds of simple, all-around healthy choices are often much more effective than rash ones such as throwing out all your BPA-lined plastic bottles because it is difficult to eliminate specific risks without introducing new ones. Some packaging manufacturers have stopped using BPA, for instance, but “what they've put in instead is less well tested and often from the same chemical family,” Zikmund-Fisher says. “Does it have fewer risks? Who knows.”
Ultimately, Zikmund-Fisher says, we need only look around to realize that there is no need to panic: the vast majority of pregnancies carried to term produce healthy children. “Look at your life and the choices you make, and do things that can make you safer easily, but don't overreact to anything,” he explains. “There are very, very few things out there that have such huge effects on our lives or our baby's lives that one teeny bit of exposure is going to make a difference.”