Does drinking alcohol during pregnancy lower child IQ?

By George Gifford

A recent study by Lewis et al, 2012, suggests that moderate alcohol intake during pregnancy can affect later IQ scores. This study is particularly striking as it suggests changes in IQ in children with pregnant mothers involved drank very small amounts, between 1-6 units a week. Additionally, there has been a real lack of conclusive evidence in this area, many studies suffering methodological flaws, making this new study particularly interesting.

Media coverage of this study was both very sensible and horrendously bad. For example, the Sun’s headline, ‘any wine and kid’s a plonker’, is grossly inaccurate and offensive to the very real effects that alcohol can have on a child’s development. In addition, there was a very defensive article in the Daily Mail, which saw the study as an affront to pregnant women, very much missing the point that science is objective.

On top of this, some articles only really half reported the study, stating simply that it found that women who drank 1-6 units of alcohol a week caused an average point drop of 1.8 IQ points in their children. Although this is sort of reported in the study, without the full picture it is misleading as it suggests some sort of predictable calculation for the amount of alcohol a pregnant woman can drink and how many IQ points their child will lose.

When looking at the specifics of the study we get a very different impression from this. Researchers identified genes involved in the breakdown of alcohol in mothers and children and found that those with genes making them better at breaking down alcohol had, on average, slightly higher IQ scores than those who did not. This effect was only found amongst the pregnant women who drank alcohol and not those who abstained, suggesting alcohol to be what caused the difference in IQ scores.

To summarise: the study showed higher genetically based efficacy in breaking down alcohol protected prenatal children from the effects of alcohol on their later intelligence.

Now the 1.8 drop actually refers to the effects of alcohol intake on IQ scores for each individual alcohol-breakdown-related gene (allele). In particular researchers focused on 4 alcohol breakdown genes in the child and 1 in the mother (all important because they code for enzymes which break down alcohol molecules- alcohol dehydrogenases).What is complicated about these genes is that some code for alcohol breakdown enzymes in the stomach, so for pregnant drinkers this means breaking down alcohol before it reaches the blood and baby, and some code for enzymes produced by the liver, which means breakdown when the alcohol is in the blood circulation. Further complicating this, some genes may play more active roles at different points in the pregnancy, genes may interact with each other, and there could be many more genes which affect the breakdown of alcohol in the mothers or prenatal baby.

The point we can take from this is that genetic differences in how well mothers and foetuses break down alcohol make alcohol’s impact of prenatal development unpredictable. This is why it is nearly impossible to know how much alcohol would be safe to drink during pregnancy, and why some guidelines suggests women should drink no alcohol at all. Certainly, you should not think that the statistic of 1.8 IQ points for every 1-6 units of alcohol per week would apply to all, not least because there is likely a big difference between drinking 1 or 6 units of alcohol a week (especially if you drank 6 units in one session- binge drinking may be particularly bad), but also because an acceptable amount for one woman and baby could be significantly damaging to another.

It can be said however, that the changes in IQ in the study were small enough for some to see as insignificant (around 3 IQ points from those judged most genetically vulnerable and those judged the least genetically vulnerable). Even looking at a more extreme experiment where children dropped 7 IQ points with mothers who drank 2 drinks per day, all the children involved were functioning in the average range of intelligence (though please don’t have 2 drinks a day if you are pregnant). Given that it is not unlikely that anyone reading this was exposed to a little bit of wine in the womb, it would be wrong to stigmatise pregnant women who had the occasional small glass of wine.

Despite being minimal however, these changes in the study in question were matched with moderate amounts of alcohol. The overall picture we get from this is that alcohol’s effect on the developing foetus cannot be seen in terms of a threshold, rather it can be seen as simply, the more alcohol you drink when pregnant-the more the child will be impaired. We know that very heavy drinking produces severe damage to the foetus particularly in terms of brain development.

With all this in mind, we can see that the National Institute of Clinical Excellence (NICE) guidelines for drinking when pregnant are really very sensible, suggesting that pregnant women ideally should not drink alcohol in the first three months, and if they do drink after this, to drink only 1-2 units once or twice a week.

Main points of this article:

  •  The study used certain genes that effect how well pregnant mothers and foetuses break down alcohol to explore the risk of alcohol to the foetus. As there are quite a few of these genes, this differs greatly from person to person, making alcohol’s effects on the foetus unpredictable.

  • The study suggests that small amounts of alcohol can have some detectable effect on developing foetuses in terms of a small reduction in IQ.

  • The NICE guidelines for drinking when pregnant are very sensible.