ACOG and the CDC have long held that there is no known safe amount, no safe time to drink, and no safe type of alcohol during pregnancy. While some women report drinking small amounts during pregnancy without apparent effects on fetal development, the children of many other women who report drinking the same amount do display some of the range of developmental effects that fall under the umbrella of fetal alcohol spectrum disorders.
A recent twin study by Hemingway et al. (2019) helps to explain these divergent outcomes. The study compared identical-twin, fraternal-twin, full-sibling, and half-sibling pairs with nearly identical alcohol exposure in utero and found that as the closeness of the genetic relationship decreased, differences in the pair outcomes increased. This study is further evidence that the same amount of alcohol is metabolized differently by two separate fetuses sharing an intrauterine environment with disparate outcomes. As a result, there is no way to predict how an individual fetus may be affected by any amount of alcohol. Thus, the safest approach is for women who are either currently pregnant or who may become pregnant to avoid drinking any amount of alcohol at all during those vulnerable times.
I screen all of my patients for risky alcohol use, including any alcohol use during pregnancy, and recommend that all obstetrical providers do the same. The ACOG Fetal Alcohol Spectrum Disorder Prevention Program provides free online trainings and resources for providers to implement screening and brief intervention for alcohol use during pregnancy.