Women who drink a glass of wine once a week throughout their pregnancy may not be harming their unborn children.
Researchers at University College London found boys born to light drinkers get higher scores in vocabulary tests.
Girls are also thought to benefit, with researchers finding 30 percent of those born to light drinkers are less likely to have emotional and peer interaction problems.
Lead researcher Dr. Yvonne Kelly said that, for some behavioral outcomes, children born to light drinkers were "less likely" to have problems compared to children of mothers who drank nothing at all.
"It may also be that light drinking mothers tend to be more relaxed themselves and this contributes to better behavioral and cognitive outcomes," Kelly added.
But chief medical officer Sir Liam Donaldson did not change his official advice to pregnant women.
He said: "Pregnant women or women trying to conceive should avoid drinking alcohol."
The researchers' findings are published in the International Journal of Epidemiology.