Scientists may soon be able to predict which women are likely to suffer from depression after giving birth.

They have found that women who suffer from severe post natal depression have higher levels of chemicals called thyroperoxidase antibodies in their bloodstream.

It could improve detection and diagnosis of depression and enable these women to get better help

Professor Victor Pop

The discovery suggests that post natal depression may not - as has been widely assumed - be caused entirely by the psychological and emotional turmoil associated with pregnancy and birth.

The discovery, from a study of 300 pregnant women by Dutch scientists, could enable doctors to identify individuals most at risk.

They could then be given extra help and support.

Researcher Professor Victor Pop, from Tilburg University, said: "This is important. It could improve detection and diagnosis of depression and enable these women to get better help."

Up to eight out of 10 new mothers are thought to suffer from postnatal depression.

Symptoms

Typically, they become weepy, irritable or slightly depressed about three or four days after the delivery.

The problem usually lasts just a few days, but about 10% of women suffer some form of clinical depression.

About four women per 1,000 who give birth have to be treated in hospital.

Up to 50 women a year commit suicide before their child's first birthday as a result of postnatal depression or other psychiatric disorders.

Sufferers of postnatal depression include the late Princess of Wales, Mick Jagger's ex-wife Jerry Hall, model Rachel Hunter, and TV presenter Judy Finnigan.

Heather Welford, an expert in post natal depression at the National Childbirth Trust, told BBC News Online that post natal depression was probably caused by a combination of social and biochemical factors.

However, she said: "A simple, non-invasive test, either biochemical or psychological, that could identify women who are more likely to develop post natal depression would be very useful."

Social support, counselling and various types of therapy have been shown to be as effective at treating post natal depression as anti-depressants.