Moderate alcohol consumption during pregnancy may reduce child's IQ - but only for some women

Children's IQ can be affected by moderate drinking during pregnancy, but only for women and children with certain gene variants. The study, which followed over 4,000 mothers and children from pregnancy up to the children's eighth birthday, is the first substantial study to use genetic variants to analyse the risk of alcohol in pregnancy.

Apart from alcohol use, other lifestyle factors can also influence a child's IQ (Intelligence Quotient)
score. In order to control for these confounders, the researchers used Mendelian randomisation. This technique groups people together according to certain gene variants, which are independent of confounding lifestyle factors. As a result, these women appear to be randomised to the genetic groups, similar to being randomised to a drug in a clinical trial.

The researchers studied genetic variants of alcohol metabolising genes that determine how fast alcohol is removed from the body. Variations in these genes cause some people to process alcohol slower than others, leading to higher levels of alcohol in the blood. As alcohol can easily pass through the placenta, this means that the fetus is also exposed to higher levels of alcohol.

'Unfortunately it's a bit of a gene lottery', said Catherine Collins, a dietitian from St George's Hospital NHS Trust in London, to the Independent. She said alcohol was likely to stay longer in the bodies of unborn babies with the susceptibility genes and do more damage. 'If your child has a particular gene profile, drinking any alcohol in pregnancy will have an effect on IQ. If your child does not have one of those identified gene variants the effect is negligible. But it's a big 'if''.

The researchers identified five gene variants that linked moderate alcohol consumption (less than 1-6 units of alcohol per week) in pregnancy to lower IQs in children: four in the children's genes, and one in the mothers'. The effect on children's IQ was only seen in women who had some alcohol during pregnancy, limiting the possibility that the studied genes affected the children's IQ through some other mechanism.

Although the study found a strong association between the gene variants and children's IQ, the effect was quite small: IQ was lowered by only 2 to 3.5 points. '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', concluded Dr Ron Gray from the University of Oxford, who led the research.