NEW YORK (Reuters Life!) – Women taking fish oil capsules during pregnancy are not more likely to stave off postpartum depression nor boost the mental development of their babies, according to an Australian study.

But they may help reduce their chances of giving birth too early and the only side effect they are likely to suffer from taking fish oil is increased belching, according to the study published in the Journal of the American Medical Association.

Researchers from the Women's and Children's Hospital in North Adelaide set out to test the effects of daily supplements of docosahexaenoic acid (DHA), which earlier studies have hinted might improve pregnancy outcomes.

They looked at more than 2,000 Australian women who received either vegetable oil or fish oil containing DHA during the second half of their pregnancy – a key time for foetal brain growth.

The pills used in the study contained 800 milligrams of DHA and 100 milligrams of another so-called omega-3 fatty acid as well.

DHA is a building block of cell membranes and is especially important in brain development.

"Before DHA supplementation in pregnancy becomes widespread, it is important to know not only if there are benefits, but also of any risks for either the mother or child," said researcher Maria Makrides in a statement.

The good news: the only side effect was belching, which was almost twice as common in women eating fish oil as in those on vegetable oil.

The bad news: fish oil didn't do much to help avoid depression, with both groups hovering around ten percent in self-reported high levels of depressive symptoms.