Thursday November 15 2012
Could alcohol in pregnancy harm your baby's brain power?
"Any wine and kid’s a plonker," is today’s Sun headline. This headline achieves a triple whammy of badness – being fearmongering, crassly offensive and, to cap it all, inaccurate.
The Sun headline – and other better reports – are based on a study of pregnant women and the impact of alcohol consumption on babies’ IQ in later life. But, as has not been made clear in many of the reports, the researchers were also looking at foetal and maternal variations in genes thought to affect the metabolism of alcohol (how long it takes for the body to break down alcohol). Researchers then looked at whether these variations had an impact on the children’s IQ at age eight.
It found that four genetic variants were strongly related to IQ score at age eight. The difference between the highest risk group and the lower risk group was estimated to be around 3.5 IQ points – which is relatively modest.
The effect was only seen among the offspring of mothers with the high-risk genetic variants who were moderate drinkers (1-6 units of alcohol a week). The children of mothers with the same genetic variants who abstained from alcohol during pregnancy did not experience a similar drop in IQ.
The findings of the research suggest that some children born to mothers with certain genetic variants are more vulnerable to the harmful effects of alcohol.
There is nothing in this study to contradict the current advice – those who are pregnant or trying to conceive are currently advised to avoid alcohol altogether, in the first three months of pregnancy.
With that in mind, the same evidence would suggest that pregnant women who have a cheeky glass of wine once a month should not stay up all night worrying that they are going to give birth to a ‘plonker’.
Where did the story come from?
The study was carried out by researchers from the University of Bristol, University of Oxford, University of Leicester and University of Nottingham in the UK, and the University of Queensland, Australia. It was funded by the charitable foundation Wellcome Trust.
The study was published in the open access peer-reviewed journal, PLoS One.
Most of the papers had problems explaining the study’s exploration of genetic variations in the risk to the child of drinking in pregnancy, opting instead for the simple warning that women who drink moderately may risk harming the child’s levels of intelligence. While this is not incorrect, it is not the whole story.
The Independent’s coverage stands out because the paper included comments from several independent experts.
What kind of research was this?
This was a cohort study following women recruited during pregnancy and their children, which aimed to find out if foetal and maternal variations in the genes thought to be responsible for breaking down alcohol in the body were related to the child’s cognitive score at age eight.
As the researchers point out, the harmful effects on the baby of heavy drinking in pregnancy are well established, but the effects of moderate drinking are less clear. Studies on this have been inconsistent in their results and may reflect problems with confounding factors such as the woman’s lifestyle, health and education. The researchers point out that studies that look at genetic variations have an advantage in that they are not associated with lifestyle factors.
When someone has an alcoholic drink, the alcohol itself (ethanol) is converted to a chemical compound called acetaldehyde by a group of enzymes. This neutralises the harmful effect of alcohol. Variations in the genes that 'encode' these enzymes lead to differences in the ability of people to metabolise ethanol. In 'slow metabolisers', peak alcohol levels may be higher and persist for longer than in 'fast metabolisers'. Theoretically, 'fast' metabolism of ethanol protects against abnormal brain development in infants because less alcohol crosses the placenta and reaches the foetus. However, the exact mechanisms remain unclear.
What did the research involve?
The researchers used data from a large, ongoing UK study investigating environmental and other factors that may affect the health and development of children. The study recruited 14,541 pregnant women of white European origin with an expected date of delivery between April 1991 and December 1992. Of these, 13,822 gave birth to a single baby. Detailed information was obtained from the mothers throughout pregnancy and information on both mother and child has been collected at regular intervals and is ongoing.
Women were asked about their alcohol consumption at 18 weeks into the pregnancy. They were asked to recall how frequently they drank in the first term of pregnancy and in the previous two weeks, or when they felt the baby first move.
The women were asked to say whether their frequency of drinking was one of the following:
- less than one unit a week
- one unit or more a week
- 1-2 units a day
- 3-9 units a day
- more than 10 units a day
One drink was specified as one unit of alcohol – equivalent to a small glass of wine or half a pint of normal-strength beer. Any woman who reported drinking at this time even if it was less than one unit a week, was classified as a drinker.
The women completed another questionnaire at 32 weeks gestation in which they were asked about their average weekday or weekend consumption.
At both 18 and 32 weeks, women were also asked on how many days during the past month they had drunk two pints of beer (or the equivalent amount of alcohol) and any woman who reported doing this was classified as a binge drinker. The researchers excluded from their analysis 269 women who reported drinking more than six units a week at any point during pregnancy, since they were interested in the effect of moderate intake on IQ scores rather than the effects of heavy drinking.
The researchers looked at differences in the genetic make-up (genotype) of both mothers and babies by examining their DNA sequencing. They selected DNA variants in four particular genes, using genotyping techniques (in both mother and baby), which have previously been shown to be associated with alcohol metabolism, intake or dependency.
Using validated statistical techniques they analysed the association between these genotypes and the IQ scores at age eight. Maternal and foetal genotypes were looked at separately. Cognitive testing was carried out on the children during a clinic visit at eight years, using a shortened version of an established intelligence test for children.
The researchers adjusted the findings for potential confounders including mothers’ education, smoking, age, marital status and class. They then took the four gene variants that were found to be related to the IQ score at age eight, to see if there was any association between these and the mothers’ reported alcohol intake during pregnancy.
Mothers who reported drinking more than one unit a day during pregnancy were excluded from analysis, leaving 4,167 women and their children who had provided enough data.
What were the basic results?
The researchers found that four genetic variants in the alcohol metabolising genes in 4,167 children were strongly related to lower IQ at age eight. The child’s IQ was on average almost two points lower for each genetic 'risk' variant they possessed.
This effect was only seen among the offspring of mothers who were moderate drinkers (1-6 units alcohol per week during pregnancy), with no effect among children whose mothers abstained during pregnancy.
A further genetic variant associated with alcohol metabolism in mothers was associated with their child’s IQ, again only among mothers who drank during pregnancy.
How did the researchers interpret the results?
The researchers say the results could have important public health implications. They say that while the effects of the genotype appear 'modest', this study involved women drinking less than one unit of alcohol a day and larger effects might be anticipated for women who drink more than this.
They say their study offers some support to the theory that even small amounts of alcohol in pregnancy may influence foetal brain development and have an effect on future cognitive outcomes.
This is a complex study looking at the relationship between moderate drinking in pregnancy, maternal and foetal genetic variants thought to affect how quickly alcohol is metabolised and later IQ in children.
It suggests that among women who drank moderately in pregnancy, four genetic variants in foetal genes (genes in the baby) related to alcohol metabolism was related to the child’s later IQ score. A further genetic variant associated with alcohol metabolism in the mother was also associated with the child’s IQ. It should be pointed out that the differences in IQ were very small – with difference between the highest-risk genetic group compared to the lowest genetic group estimated to be around 3.5
Ignoring some of the inaccurate headlines, this study still has limitations that could affect the reliability of its results, notably:
- it relied on women self-reporting how much they drank
- IQ in the children was only tested once
- only certain genetic variants were selected for analysis, when it is possible that several others are involved in determining how far alcohol may affect the foetus
A further limitation of this study is that it groups together mothers who reported drinking less than one unit a week with those who drank six units a week. This makes it difficult to determine from this data if there is a safe level of drinking during pregnancy.
Whether moderate drinking in pregnancy can affect foetal development is for the moment uncertain.
This study suggests that genetic variations in the mother and baby may play a role, but further research is needed to confirm its findings.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on twitter.