Drinking one or two units of alcohol a week during pregnancy does not raise the risk of developmental problems in the child, a study has suggested.
Official advice remains that women abstain completely during pregnancy.
A study of more than 11,000 five-year-olds published in the Journal of Epidemiology and Community Health found no evidence of harm.
There were more behavioural and emotional problems among the children of heavy-drinking women.
When a pregnant woman drinks alcohol, it passes through the placenta and reaches the baby, which is less well-equipped to break it down.
Researchers have strongly linked heavy drinking to an increased risk of lifelong damage.
However, the evidence about the risks to lighter drinkers has been far less clear.
The study, led by University College London but involving three other UK universities, is the second by this group examining large numbers of children looking for signs that brain development had been affected.
No extra risk
The first had found no evidence of problems at age three, but the latest study extended the checks until school age to make sure nothing had emerged later.
The same result appeared, with no extra risk of behavioural and emotional issues compared with children whose mothers had abstained during pregnancy.
In fact, the children born to light drinkers appeared slightly less likely to suffer behavioural problems, and scored higher on cognitive tests, compared with women who stopped during pregnancy.
Dr Yvonne Kelly, from UCL, said : "There's now a growing body of robust evidence that there is no increase in developmental difficulties associated with light drinking during pregnancy."
She said that women could make "better decisions" with this information.
However, a spokesman for the Department of Health said that its advice would remain unchanged.
"We are continually taking account of evidence and welcome this further report.
"However, the research does not lead to any change in the current UK wide advice that pregnant women and those trying to conceive should, as a precautionary measure, avoid alcohol."
Additional advice from the National Institute of Health and Clinical Excellence urges women to avoid alcohol, particularly in the first three months of pregnancy.
This advice was backed by Chris Sorek, the chief executive of alcohol awareness charity Drinkaware.
He said: "Despite these findings, it is important to remember that 'light drinking' can mean different things to different people.
"There is a risk that if pregnant women take this research as a green light to drink a small amount, they could become complacent, drink more than they think they are and inadvertently cause harm to their unborn child.
"Excessive drinking during pregnancy can carry serious consequences and lifelong damage to children and should be avoided."
But Dr Tony Falconer, the president of the Royal College of Obstetricians and Gynaecologists, said that while the "safest choice" was abstinence, the current evidence suggested that drinking one or two units, once or twice a week was acceptable.
"The key public health message, whether or not a woman is pregnant, is that light drinking is fine, but heavy and binge drinking should be avoided."