Women who drink even moderate amounts of alcohol while pregnant may risk lowering their child’s intelligence levels, according to a study by British scientists.
Advice to pregnant women about drinking is contradictory, with some guidelines recommending no alcohol at all and others suggesting the odd drink now and then is safe.
But in a study described as “hugely important” by one expert, researchers using genetic analysis of more than 4,000 mothers and children found that drinking between one and six units of alcohol a week during pregnancy can lead to lower Intelligence Quotient (IQ) scores by the time a child is eight.
“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 Sarah Lewis of Bristol University. “This is evidence that even at these moderate levels, alcohol is influencing foetal brain development.”
This study used genetic data from women and children who were part of another study called Children of the 90s.
Since the individual genetic variations that people have in their DNA are not connected to lifestyle and social factors, this kind of study avoids potential complications.
Most previous studies have used observational evidence, but experts say this can be misleading because, for example, mothers who drink in moderation while pregnant are typically also well educated, have good diets and are unlikely to smoke – all factors linked to higher IQ in children and which could mask any negative effects of alcohol.
A US study published in July found that older, educated women are more likely to drink while pregnant.
This study, published in the journal Plos One, used a new technique analysing the genetic variants which modify the effects of alcohol exposure levels.
When a person drinks alcohol, ethanol is converted to acetaldehyde by a group of enzymes, the researchers explained.
Variations in genes that ‘encode’ these enzymes lead to differences in a person’s ability to metabolise ethanol, so in “slow metabolisers”, alcohol levels may be higher for longer than in “fast metabolisers”.
The mothers were asked to record their alcohol consumption at various stages during pregnancy, and one drink was specified as one unit of alcohol.
The results showed that four genetic variants in alcohol-metabolising genes among the 4,167 children were strongly related to lower IQ at age eight.
The child’s IQ was on average almost two points lower per genetic variation they had.