Research showing that children of women who drank as little as two glasses of wine a week during pregnancy had lower IQs has prompted calls for mothers-to-be to avoid alcohol.

The study, by academics at Bristol and Oxford universities, found that offspring of women who consumed between one and six units of alcohol a week were 1.8 IQ points less intelligent when they were tested at the age of eight than peers whose mothers had abstained.

"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," said Dr Sarah Lewis, the report's main author. "This is evidence that, even at those moderate levels, alcohol is influencing foetal brain development."

Dr Ron Gray, a co-author, said the study, which used genetic variation in alcohol metabolism to examine in utero exposure, was complex but contained a simple message. "Even moderate amounts of alcohol during pregnancy can have an effect on future child intelligence. So women have good reason to choose to avoid alcohol when pregnant," he said.

The Department of Health advises pregnant women and mothers-to-be not to drink but, if that is not possible, to limit themselves to one or two units once or twice a week and to never get drunk.

Organisations representing specialist groups of doctors, such as paediatricians and obstetricians, reiterated their support for total abstinence because of potential harm to unborn children, including fetal alcohol syndrome, which affects an estimated 6,000 newborn babies a year.