Drinking in the third trimester of pregnancy—even just a glass or two of alcohol a week—may lower a baby's IQ by a few points, according to new research. The issue has been long debated by doctors, but a new study led by Ron Gray, an epidemiologist at the University of Oxford, suggests that light drinking does harm a baby's brain development. Researchers tested for slow metabolizing genes in thousands of pregnant women—some who abstained from alcohol during pregnancy, and others who drank the equivalent of a half pint to three pints of beer (or three small glasses of wine) a week. Eight years later, researchers examined the IQ's of 4,167 of these women's children; they found across the board that women who drank lightly or not at all during pregnancy gave birth to children with higher IQ's. "This is good evidence to implicate moderate drinking during pregnancy having an effect on childhood IQ at age 8," says Gray. "Some women are going to be genetically more vulnerable or resilient than others to the effects of alcohol on the fetus, but we don't know who those people are."

However, the results are not entirely conclusive. The study's non-drinkers were richer, older and more educated than their drinking peers, which may have skewed the results. Also, research into the controversial issue of drinking during pregnancy has resulted in a dramatic range of findings over the past few years. One study has linked a glass of wine a day to premature births, while another claims light drinking does not in fact harm a baby's brain development. One study even found that women who drank lightly during pregnancy gave birth to children with higher vocabularies.