Drinking in moderation through pregnancy does not harm a baby's neurodevelopment, according to a study by the University of Bristol's School of Social and Community Medicine. However, this may be because women who are more likely to drink moderately are from an affluent background.

Almost 7,000 10-year-olds were asked to take part in balance tests, which are an indicator of prenatal neurodevelopment.

The drinking habits of their mothers had been recorded during and after pregnancy, with those who drank three to seven glasses of alcohol a week classed as moderate drinkers.

Social advantage could be a large factor in the findings, as the research found mothers who were more affluent and better educated were more likely to drink in moderation.

Mothers from a working class background were more likely to abstain from alcohol through pregnancy, to drink heavily or binge drink.

Children whose mothers consumed the equivalent of a glass of wine a day were able to balance as well as those who had not been exposed to alcohol in the womb.

Results showed that after taking account of influential factors such as age, smoking and previous motherhood, low to moderate alcohol consumption did not seem to interfere with balance.

But better balance was associated with greater levels of affluence and educational attainment.

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Professor John Macleod, from the University of Bristol's School of Social and Community Medicine, led the study, which has been published by the journal BMJ Open.

He said: "In this group of mothers, moderate alcohol intake was a marker for social advantage which could be a key factor in better balance.

"It could possibly override subtle harmful effects of moderate alcohol use.

"The supposed benefits we saw are not the effects of alcohol, they are effects of middle classness."

"There weren't many heavy drinkers. We know that heavy drinking during pregnancy has bad effects on a developing fetus.

"The moderate drinkers consumed an equivalent of up to one glass of wine a day.

"When we compared moderate drinkers with women who didn't drink at all we actually found that in relation to a number of different tests of balance the children of moderate drinkers appeared to do better.

"However, we also found that the women who moderately drank compared to women who didn't drink tended to be more middle class.

"They were more socially advantaged. Having a middle class mum compared to having a working class mum is likely to advance a child in a lot of ways.

The 10-year-olds were part of the University of Bristol's Avon Longitudinal Study of Parents and Children (ALSPAC).

ALSPAC has been tracking the long-term health of around 14,000 children born between 1991 and 1992 to women living in the former Avon region of the UK.

70% of the mothers drank no alcohol while pregnant. One in four drank between one and seven glasses a week.

Just 4.5% drank seven or more glasses a week. Around one in seven of these mothers were classified as binge drinkers, consuming four or more glasses at once.

The mothers were also assessed four years after the pregnancy and 28% said they did not drink at all, while over half consumed between three and more than seven glasses a week.

Professor MacLeod said: "The way we investigated this further was to look at genes. People who carry a certain gene are for more likely not to drink alcohol on average.

"If it was really true that using a small amount of alcohol during pregnancy benefitted children's balance then we would expect those with mums who had the gene to have worse balance.

"We didn't see any evidence that babies of mothers with this gene had worse outcomes than those who drank.

"There was a weak suggestion that children of mothers with the gene had better balance but our study was too small to show this reliably."

The Royal College of Midwives said expectant mothers should still steer clear of alcohol, however.

Professional policy adviser Janet Fyle said: "We recognise that this is useful research. However, there is also a large amount of evidence suggesting that the cumulative effects of alcohol consumption during pregnancy can harm the developing foetus.

"Our advice continues to be that for women who are trying to conceive or those that are pregnant it is best to avoid alcohol."

A spokesman for the Department of Health said: "Drinking during pregnancy can be associated with miscarriage, fetal alcohol syndrome and low birth weight.

"Our advice remains that women who are trying to conceive or are pregnant should avoid alcohol. If women choose to drink, to minimise the risk to the baby they should not drink more than one to two units of alcohol once or twice a week and should not get drunk."