This is the first study, to our knowledge, on the role of ADH variants on alcohol drinking in women just before and during pregnancy. Strong external pressures exist for pregnant women to modify their behavior and quit alcohol (30–32). Such pressures might highlight any existing genetic component to drinking behavior, through homogenization of some of the concurrent social determinants of alcohol drinking. However, the extreme-case scenario is that they could result into everybody abstaining from alcohol regardless of their genotype, thus overriding genetic effects. Indeed, we found that carriers of the rs1229984 A allele (ADH1B), who before pregnancy were both more likely to abstain and drink less on average, during pregnancy and in particular in the first trimester, were still drinking less, and they were less likely to binge drink and more likely to have stopped drinking altogether. This supports the use of the rs1229984 variant as a candidate instrument for alcohol drinking (versus very little or no drinking) around the time of conception and even more so for binge drinking during pregnancy. This instrument would be highly specific to
