Light drinking during pregnancy does not harm a young child's behavioural or intellectual development, reveals research published online in the Journal of Epidemiology and Community Health.
A previous study of 3 year olds drew similar conclusions, but the authors wanted to rule out possible delayed "sleeper" effects in older children.
They used data from the Millennium Cohort Study - a large study tracking the long term health of children born in the UK - drawing on a representative sample of 11,513 children born between September 2000 and January 2002.
Participants' mothers were interviewed in person about their drinking patterns while pregnant and other social and economic factors likely to have an impact on a child's development, when their children were aged just 9 months.
There are no widely agreed criteria on how to categorise patterns of alcohol consumption, but the authors chose those outlined in the government's National Alcohol Strategy.
The mothers were classified as teetotal; those who drank but not in pregnancy; light (1 or 2 units a week or at any one time); moderate (3 to 6 units a week or 3 to 5 at any one time); and binge/heavy (7 or more units a week or 6 at one sitting).
The mums were quizzed about their children's behaviour at the age of 3, and then their behavioural and intellectual development were formally assessed at the age of 5.
Just under 6% of the mums never drank, while 60% chose to abstain just for the period of their pregnancy. Around one in four (just under 26%) said they were light drinkers. One in 20 (5.5%) were moderate drinkers and 2.5% were heavy or binge drinkers during their pregnancy.
Across the entire sample, boys were more likely than girls to have more developmental problems, overall. And they were more likely to have behavioural issues, be hyperactive, and have issues with their peers. Girls were more likely to have emotional issues.
Girls achieved higher average scores than the boys on their cognitive abilities - measured by a vocabulary test, pinpointing visual similarities, and making patterns.
Children whose mothers were heavy drinkers were more likely to be hyperactive, and have behavioural and emotional problems than children whose mothers chose not to drink during pregnancy.
But there was no evidence to suggest that the behavioural or intellectual development of children whose mums were light drinkers during the pregnancy had been compromised.
Children born to light drinkers were 30% less likely to have behavioural problems than children whose mothers did not drink during pregnancy.
After taking account of a wide range of influential factors, these children achieved higher cognitive scores than those whose mums had abstained from alcohol while pregnant.
Explore further: Changing diagnosis codes will challenge emergency medicine