Whereas the fetal consequences of heavy alcohol intake during pregnancy have been clear for some time (1), the effect of moderate drinking remains controversial (2). The advice to pregnant women is generally to abstain, since no amount of alcohol is known to be safe (3). However, this is based on a precautionary principle rather than on solid evidence. Even where associations have been confirmed, these have generally been weak (4) and could still be due to residual confounding (5,6) and under-reporting of prenatal alcohol use (7,8). Both of these potentially interfere with establishing causality of the associations of maternal alcohol intake with various outcomes [from fetal growth and neurodevelopment (9) to childhood mental health problems such as hyperactivity or inattention (10) or conduct disorder (11)] and deriving evidence-based messages for the public.
