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UK study finds even drinking in moderation during pregnancy can affect a child's IQ
14th November 2012 - Relatively small levels of exposure to alcohol while in the womb can influence a child's IQ, according to a new study led by researchers from the universities of Bristol and Oxford.
The report's main author, Dr Sarah Lewis, said in a press statement: "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 foetus to clear this alcohol. This is evidence that even at these moderate levels, alcohol is influencing foetal brain development."
Lifestyle vs genes
Using data from more than 4,000 mothers and their children who are part of the long-term health project 'Children of the 90s study', the researchers used genetic variation in alcohol metabolising genes to investigate the effects of moderate (less than 1-6 units of alcohol per week) drinking during pregnancy
Previous studies have relied on observational evidence which often finds that moderate drinking is beneficial compared to abstention. However, the researchers say this is because mothers who drink in moderation during pregnancy are typically well educated, have a good diet and are unlikely to smoke - all factors which are linked to higher IQ in the child and which mask any negative effect that exposure to alcohol may have.
Since the individual variations that people have in genes are not connected to lifestyle and social factors, this new study removed that potential complication.
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 modification they possessed.
However, this effect was only seen among the children of women who were moderate drinkers. There was no effect evident among children whose mothers abstained during pregnancy, strongly suggesting that it was the exposure to alcohol in the womb that was leading to the difference in child IQ.
Alcohol consumption levels
Alcohol, like carbon monoxide from cigarettes, passes easily through the placenta from the mother's bloodstream into her baby's blood. The blood alcohol level (BAC) of the foetus can become equal to, or greater than, the blood alcohol level of the mother and because the foetus cannot break down alcohol the way an adult can, its BAC remains high for a longer period of time.
The mothers' alcohol intake was based on questionnaires completed when they were 18 and 32 weeks' pregnant. One drink was specified as one unit of alcohol.
Any woman who reported drinking, even if it was less than one unit per week either in the first trimester or when she felt the baby first move was classified as drinking during pregnancy.
The children's IQ was tested when they were eight years old.