Drinking low or moderate amounts of alcohol in early pregnancy does not appear to cause developmental problems in young children, new research suggests.
But drinking high levels of alcohol weekly were linked to lower attention spans in five-year-old children, the study found.
It's known that heavy drinking during pregnancy can be harmful to a baby's physical and emotional development. Drinking in the early stages has also been linked to a higher risk of miscarriage.
But less is known about the effect on children whose mothers drink low or moderate amounts of alcohol while pregnant.
The researchers produced five papers which looked at the effects of low, moderate, high and binge drinking on IQ, attention span, executive functions such as planning, organisation and self-control in five-year-old children.
Some 1,628 pregnant women, average age 31, were recruited for the studies when they first visited an antenatal clinic. They were then questioned about how much their alcohol consumption, and their weekly drinking habits recorded.
Low alcohol consumption was defined as one to four drinks, moderate as five to eight and high levels as nine or more. Binge drinking was defined as having five or more drinks on a single occasion. Pregnant women who did not drink were also included in the study for comparison
In Denmark, one standard drink has 12g of pure alcohol, whereas one unit in the UK has 7.9g. A small (125ml) medium-strength glass of white wine has approximately 1.5 units.
Overall, the researchers found that low to moderate weekly drinking in early pregnancy had no significant effect on the neurodevelopment of children aged five years, and neither did occasional binge drinking.
No differences in IQ and other tests were seen in children whose mothers consumed one to four or five to eight drinks a week during pregnancy compared with mothers who did not drink any alcohol.
But consuming nine or more drinks a week was linked with lower attention spans among five-year-old children.
The studies are published in the British Journal of Obstetrics and Gynaecology.
The study authors said: "High prenatal exposure to alcohol has consistently been associated with adverse effects on neurodevelopment.
"Areas such as intelligence, attention and executive functions have been found to be particularly vulnerable.
"Our findings show that low to moderate drinking is not associated with adverse effects on the children aged five.
"However, despite these findings, additional large scale studies should be undertaken to further investigate the possible effects."
Currently the Department of Health recommends that women should not drink alcohol while pregnant, but if they choose to do so, advises drinking no more than one to two units of alcohol once or twice a week and to avoid getting drunk or binge drinking.
The National Institute for Health and Clinical Excellence (NICE) advises pregnant women to avoid drinking any alcohol in the first three months in particular, because of the higher risk of miscarriage.
Patrick O’'Brien, consultant obstetrician and a spokesperson for the Royal College of Obstetricians and Gynaecologists (RCOG) said: "These findings suggest low to moderate drinking has no significant effect on children aged five.
"However, this does not mean that women can use this as an excuse to indulge in more than the recommended amount in the UK.
"The RCOG advises that if a woman falls pregnant, she should abstain from alcohol.
"However, if she would like to have a drink, the current evidence shows that one or two units, once or twice a week, is acceptable after 12 weeks of pregnancy.
"Pregnant women should consult their midwives and GPs if they have any concerns about their alcohol intake."