Drinking during pregnancy is still the number-one preventable cause of birth defects in the U.S. The problems that result from fetal alcohol exposure—at any stage of pregnancy, including before the woman knows she is pregnant—can appear any time during childhood and last forever.
That said, eight percent of pregnant women in the U.S. report drinking. Among the often complex reasons for that, some studies have shown ambiguity with regard to mild drinking. Some research has said it could even be beneficial. Recommendations are at odds from doctors and government agencies. In most countries, including the U.S., the reigning guideline is total abstinence. The official position of the National Institutes of Health:
Research shows that binge drinking, which means consuming four or more drinks per occasion, and regular heavy drinking put a fetus at the greatest risk for severe problems. But even lesser amounts can cause damage.
But in the U.K., for example, the recommendation condones low to moderate consumption. Women who are or are planning to become pregnant, says the U.K. Department of Health, "should not drink more than one or two units of alcohol once or twice a week, and should avoid episodes of intoxication.” In the U.K., 63 percent of pregnant women report drinking.
A working paper out today from the National Bureau of Economic Research offers more nuance on this question, looking at childhood academic achievement, and says the U.K. should reconsider its recommendation:
Simple correlations between alcohol exposure and child academic achievement show somewhat ambiguous results, with exposure to wine having a positive association, but exposure to beer being negative. Binge drinking is bad for the child, but a longer duration of exposure is positively associated with the child’s academic performance. However, we present clear evidence of the endogeneity of alcohol intake, showing a strong social gradient in maternal alcohol consumption, with mothers of higher socioeconomic status more likely to drink, and in particular, drink wine. In contrast, beer consumption is associated with lower education and worse mental health. ...
We cannot make any strong statements about the specific effects of low-to-moderate versus excessive prenatal alcohol intake, though the analyses suggest that both negatively affect child academic attainment.
Basically the NBER report is saying studies that seem to condone or recommend mild drinking during pregnancy reflect statistical error and confounding social factors, and no amount of alcohol is advisable.
I share this not to panic parents retroactively and hope it doesn't. No use in that. This research offers one considerate voice on a weighty topic of ongoing understanding.