Mums-to-be, you may want to rethink that one glass of chardonnay you have at supper. According to a new study by academics at Bristol and Oxford universities, pregnant women who consume as little as one unit of alcohol per week risk lowering their unborn child’s intelligence levels.

Alcohol in pregnancy: The controversy

While all experts agree that alcohol abuse during pregnancy causes foetal alcohol syndrome, some official guidelines advocate total abstinence whereas others have declared the occasional drink harmless. This debate is due to conflicting evidence from previous studies — it is difficult to separate drinking from other social and lifestyle factors that can influence findings.

However, British researchers, who utilised genetic data from more than 4000 mothers and their children, found that even minimal exposure to alcohol in the womb could lead to cognitive deficits by the child’s eighth birthday, as shown by lower Intelligence Quotient (IQ) scores.

“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 foetus to clear this alcohol,” said lead author Sarah Lewis in a press release. “This is evidence that even at these moderate levels, alcohol is influencing foetal brain development.”

Study details

The scientists used data from a previous research, ‘the children of the 90s study’, also known as the ALSPAC study, in which 14,541 women were enrolled. Questionnaires were completed by the women to determine their drinking habits, or lack thereof, during their 18th and 32nd weeks of gestation. Moderate alcohol consumption was defined as intake of less than 1 to 6 units of alcohol per week. Heavy drinkers were excluded.

One unit of alcohol equals half pint of ordinary strength beer or 25ml of spirits while a small 125ml glass of wine contains around 1.5 units of alcohol.

In this first-of-its-kind study, Lewis and colleagues considered data from 4167 children to investigate genetic variations in genes that metabolise alcohol. Since DNA variants are not influenced by lifestyle and socio-economic components, this genetic approach eliminates potential confounders.

At age 8, cognition levels of the children were measured using a shortened version of the Wechsler Intelligence Scale for Children. The study was published in PLOS ONE.

How genes affect alcohol metabolism

When alcohol is ingested, body enzymes convert it to acetaldehyde. Differences in genes that “programme” these enzymes explain why some individuals are able to metabolise alcohol more efficiently than others. Those who metabolise alcohol slowly experience higher blood alcohol content for a greater length of time.

Since alcohol in the mother’s blood rapidly reaches her baby via the placenta, scientists believe that slow ethanol metabolism predisposes the foetus to abnormal brain development subsequent to longer foetal alcohol exposure.

Study findings

The researchers uncovered a significant association between 4 genetic variants in alcohol-metabolising genes and lower IQ in children. For each genetic variant, they found a 2-point drop in IQ, an effect not observed among children of women who were teetotallers. This strongly suggests that foetal alcohol exposure is behind the IQ disparity, the researchers said.


    Lewis et al (2012) Fetal alcohol exposure and IQ at age 8: evidence from a population-based birth-cohort study. PLoS One. 7(11):e49407.