There is “surprisingly limited” evidence that light to moderate drinking during pregnancy poses a risk to unborn babies, according to a new study published in the British Medical Journal. Researchers caution, however, that this is not necessarily because moderate drinking during pregnancy is safe—it’s because the body the research on anything short of binge drinking is too sparse for experts to draw conclusions one way or another.
“We know that heavy and binge drinking can cause fetal alcohol syndrome, but the effects of lighter drinking on offspring were not clear,” coauthor on the study Abigail Fraser, a professor of epidemiology at the University of Bristol in the UK, told Fatherly. “The dearth of studies that have actually looked at the potential effects of light drinking was surprising.”
The risks of heavy drinking during pregnancy are well-documented. Studies show that consuming more than seven drinks per week is associated with increased risk of birth defects, behavioral problems, and poor motor skills, not to mention fetal alcohol spectrum disorder. Experts agree that there’s no scientific case to made for pregnant women binge drinking or drinking heavily. But whether a glass or two of wine poses any danger is far less clear. Absent any compelling evidence of safety (or harm), medical organizations generally encourage women to err on the side of caution. The Centers for Disease Control and Prevention, for instance, controversially maintains that all sexually active women who do not use birth control should avoid alcohol. The UK’s National Health Service made a similar recommendation for anyone trying to get pregnant.
Fraser and her team reviewed more than 5,000 scientific studies, in an attempt to tease out an evidence-based approach. Out of the 5,000 articles available, however, the researchers only identified 26 studies of light drinking in pregnancy and only two of these were randomized, controlled trials—the gold standard of medical evidence. Although isolated studies suggested that light drinking could cause preterm birth and low birth weight, “due to the small number of studies included for any given outcome, it was impossible to formally investigate the effect of incomplete adjustment for some (or all) of these confounders,” the authors write. In other words, there’s just not enough data to draw meaningful conclusions.
Does this mean light drinking during pregnancy is safe? Not exactly. “The study authors correctly point out the limitations of their findings—the relatively small number of included studies,” Michael E. Charness of Boston University School of Medicine told Fatherly. Other obvious limitations are that there’s such strong stigma against drinking during pregnancy that some women may be reluctant to admit that they imbibe. The study also failed to look at fathers, whose drinking could have harmful epigenetic effects, he notes. Far from declaring just one drink safe, the study underscores that it may not be possible to determine a scientifically safe amount of alcohol for pregnant women (at least, absent more research). Which means that it may be better for expectant mothers to play it safe for nine months. As Charness puts it: “Absence of proof of a deleterious effect of low prenatal alcohol exposure isn’t proof of absence—or proof that alcohol is safe.”