Despite contradictory advice to pregnant women about alcohol consumption, the Centers for Disease Control and Prevention advocates complete abstinence during pregnancy and calls alcohol consumption the leading cause of preventable birth defects and developmental disabilities. A new study adds credence to the CDC’s advice, suggesting that even a small amount of alcohol during pregnancy can lower IQ levels in children.

Researchers from the universities of Bristol and Oxford led the Children of the 90s Study. They used genetic variation as a way to study the effects of moderate alcohol consumption during pregnancy. Over 14,000 women were surveyed during the 18th and 32nd weeks of pregnancy regarding their drinking habits, and over 4,000 children born to these women became the subjects of the study. The use of genetic variation for the study removed the potential complication of lifestyle and social factors that could have had an impact on the results of the study.

Even moderate amounts of alcohol during pregnancy can have an effect on future child intelligence. So women have good reason to choose to avoid alcohol when pregnant.

Pregnant women who reported consuming one to six drinks a week were considered moderate drinkers and included in the study. Women who reported drinking more than that or who reported consuming two drinks on one occasion were not included in the study.

The researchers looked for genetic variants in genes that metabolize alcohol. Among the children born to moderate drinkers, they found four genetic variants in alcohol-metabolizing genes that were strongly linked to a lower IQ in children once they were eight years old. Each genetic variant caused a 2-point drop in IQ. Children of non-drinking mothers did not exhibit this effect, suggesting that exposure to alcohol caused the difference in IQs.

Dr. Sarah Lewis, a senior lecturer in genetic epidemiology at Bristol University, said, “Our results suggest that even at levels of alcohol consumption which are normally considered to be harmless, we can detect differences in childhood IQ, which are dependent on the ability of the fetus to clear this alcohol. This is evidence that even at these moderate levels, alcohol is influencing fetal brain development.”

Dr. Ron Gray, who led the research, said, “This is a complex study but the message is simple: even moderate amounts of alcohol during pregnancy can have an effect on future child intelligence. So women have good reason to choose to avoid alcohol when pregnant.”

One in 13 women drink moderately while pregnant, according to the CDC. Several recent studies found that low to moderate levels of alcohol intake during pregnancy may not cause any damage to children, but the bottom line, according to the CDC, is that it’s not worth the risk. It urges women to avoid alcohol during pregnancy, saying there is no known safe amount.

The study is published in PLoS ONE.