Women who drink even moderate amounts of alcohol while pregnant may risk harming their child's intelligence levels, according to a new study.
Advice to pregnant women about drinking is contradictory, with some guidelines recommending no alcohol at all and others suggesting the odd drink now and then is safe.
But researchers using genetic analysis of more than 4,000 mothers and children found that drinking between one and six units of alcohol a week during pregnancy can lead to lower Intelligence Quotient (IQ) scores by the time a child is eight.
"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," Sarah Lewis of Bristol University, who led the study, said.
"This is evidence that even at these moderate levels, alcohol is influencing foetal brain development."
Mother-of-one Toni Denholme, 26, from Newcastle, said doctors gave her mixed messages on drinking during pregnancy.
"The doctors kind of said it was OK to drink in moderation, it wasn't as harmful as smoking or anything, but ideally not to, but there wasn't a 'don't, definitely don't drink'."
Gwen Jones, who is expecting her first child in April, said: "There's so much ambiguous advice out there what you can do what you can't do what you should and shouldn't do, so something that comes out medically and says 'definitely do not do it, it's going to harm your child', I think is brilliant."
The study used genetic data from women and children who were part of another study called the Children of the 90s study.
"This is a complex study but the message is simple, even moderate amounts of alcohol during pregnancy can have an effect on future child intelligence," said Ron Gray of Oxford University, who was part of Ms Lewis's team.
David Nutt, a professor of neuropsychopharmacology at Imperial College London, said: "Even though the IQ effects are small, if at all possible women should avoid ethanol in pregnancy as it's a known toxin."