A couple of drinks several times a month damage an unborn child's future school performance, according to an Australian-led study.
There is a clear link between a pregnant mother's alcohol consumption and her child's academic outcomes, says lead researcher Dr Rosa Alarti from the University of Queensland.
She and colleagues studied NAPLAN-style test results of thousands of 11-year-old children in England to assess the impact of alcohol in the first 18 weeks of pregnancy.
They show children whose mothers regularly drink two 150ml glasses of wine or two stubbies underperform compared with their peers, according to an article published in the journal Plos One.
The more frequently women drink these quantities, the more likely their children are to underperform, says Dr Alati, an associate professor at the university's school of population health.
"Once in a month has a lower impact than 10 times in a month."
The study rules out other influencing factors such as smoking and shows fathers who consume similar amounts do not affect their children's performance.
Co-author Dr Ron Gray from Oxford University says alcohol consumed during pregnancy could have a toxic effect on the developing brain.
"In this study that translates into poorer academic outcomes at age 11."
Although half a glass of wine had no affect on the test results, Dr Gray says: "It remains unclear whether any amount of alcohol is safe in pregnancy. The safest plan is to avoid it."