They plan to quiz almost 100,000 women on their feelings before and after the birth of their babies.

It's probably the most important time to try and prevent depression because it's the start of a child's life

Professor Anne Buist

The National Postnatal Depression Program aims to come up with new ways of identifying and combating the condition that afflicts one in seven women after giving birth.

It will screen pregnant women across Australia and follow their progress over the next three and a half years.

Screening of the first of 4,500 women began at Werribee Mercy Hospital in the eastern state of Victoria on Tuesday.

Professor Anne Buist, of the University of Melbourne and the programme's national coordinator, said the study would investigate whether postnatal depression began during pregnancy.

Public awareness

It would also aim to increase public and professional awareness as well as improving early identification and care.

She said: "It's probably the most important time to try and prevent depression because it's the start of a child's life.

"We know from a number of studies that the children of depressed women may be at a higher risk of poor developmental outcomes."

Professor Buist estimated that postnatal depression affected up to 15% of women - but in many cases went undiagnosed.

She said two-thirds of women who suffered from postnatal depression may never come to treatment. Those who did often only got help after a second baby.

However, she said it was necessary to distinguish between "normal" problems adjusting to motherhood and a genuine depressive illness requiring treatment.

"There's a lot of confusion about the 'blues', or normal difficulties with having a baby, and depressive illness.

"It's the number of symptoms, the severity of symptoms and how long they've gone on for."