It is common for women to keep drinking while pregnant, according to a study of almost 18,000 women in Australia, New Zealand, Ireland and the UK. But most women consume alcohol at low levels and the number of pregnant women who drank heavily was small.
The study, published in the online journal BMJ Open, found that women drank across all social strata, but that smokers were more likely to be drinkers. It also found that non-white women were less likely to drink than white women, and that younger women (30-39) were less likely to drink than older women.
The findings were based on three studies: Growing Up in Ireland; the Screening for Pregnancy Endpoints study; and the Pregnancy Risk Assessment Monitory Systems study.
The amount of alcohol consumed varied significantly between the studies. For example, depending on the study, a range of 15% to 70% of women reported drinking one to two units a week during the first three months (first trimester) of their pregnancy. In the second and third trimester the number of reported units of alcohol consumed dropped substantially.
All three studies showed that the strongest predictor of a heightened risk of drinking alcohol during pregnancy was smoking, with 17% to 50% of smokers more likely to drink while pregnant.
The researchers say that most gudielines advise women to stop drinking during pregnancy.