Researchers say more women may be vulnerable to depression during pregnancy than in the widely acknowledged condition known as postpartum depression.

Dr. Jonathan Evans at the University of Bristol led the study that found women reported higher levels of depression symptoms during pregnancy than after having a baby.

The researchers had more than 12,000 pregnant women fill out a series of mood questionnaires. The women were followed from 18 weeks into their pregnancy through to eight months after childbirth.

The study found the riskiest period to be 32 weeks into pregnancy. At that time, 13.5 per cent of women reported symptoms of depression.

That's compared to 9.1 per cent eight weeks after birth, and 8.1 per cent eight months post-partum.

Largely untreated

The researchers say depression during pregnancy has been relatively neglected by the health profession. They say the common belief is that pregnancy actually protects women against depression.

They say treating the condition could be important for both mother and the fetus and that using antidepressant medications may outweigh the risks for pregnant women with severe depression.

They also note there are non-drug treatments available to treat mild to moderate depression.

Potential bias

The authors say that since responding to the questionnaires was voluntary, more depressed women were less likely to answer all four questionnaires sent out during their pregnancy.

So the number of severely depressed women may be underestimated, potentially biasing the results.

The study is published in the British Medical Journal.