KEY POINTS:
The most severe form of postnatal depression, which has been linked to suicide and infanticide, could be genetic, researchers have found.
And a separate piece of research claims that more women than suspected could be afflicted with postnatal depression Up to 17,250 late-onset cases a year in Britain go undetected, this study suggests.
It was believed that the mood disorders affecting up to 75 per cent of new mothers were caused by the women's circumstances, personality and hormonal changes.
But according to a study by Cardiff University in Wales, Birmingham University in central England and Trinity College, Dublin, financed the Wellcome Trust medical charity, the most severe form of postnatal depression, postpartum psychosis, has a genetic cause.
The study is now working to isolate the gene, which will enable doctors to identify and treat high-risk women before they become ill.
New mothers can be affected by a spectrum of mood disorders. But while most women have "baby blues" - a short period of tearfulness and tiredness after childbirth - postnatal depression is a more severe, long-lasting condition which affects 10 to 15 per cent of women and can prevent mothers bonding with their babies and cause suicidal thoughts.
If left untreated, it can affect the short or long-term development of the baby.
The effect on mothers can also be devastating. Women are 23 per cent more likely to be admitted to a psychiatric unit in the 18 months after giving birth than at any other time in their lives.
Suicide is a leading cause of maternal death in the UK; most attempts are made by those stricken by an abrupt onset of postnatal depression.
Victims include actor Gwyneth Paltrow and model Elle Macpherson, who has spoken of the extreme depression she experienced after the birth of her second child, Aurelius Cy, in 2003. Actor Brooke Shields had visions of her newborn baby Rowan being thrown against a wall.
The most serious form of maternal depression affects about one in 500 new mothers. Although rare, the condition has been associated with suicide and infanticide.
"Postpartum psychosis is classed as among the most severe episodes of illness seen in clinical practice," said Dr Ian Jones, head of psychological medicine at Cardiff, who led the study into the DNA of families in which at least one woman had suffered postpartum psychosis.
"The consequences for the mother, infant and family are so serious that such episodes require close attention, often including hospitalisation."
In a paper published in this month's issue of the American Journal of Psychiatry - out this week - Dr Jones present his evidence that women with a particular recessive gene are susceptible to postpartum psychosis.
His team will now carry out the first systematic genome scan to localise the genes that influence a woman's susceptibility to bipolar affective puerperal psychosis.
"It is hoped that identifying these factors will lead to improvements in the management of women who will become ill at this time and will increase understanding of affective disorders in general," he said.
In a separate study, to be published in Bipolar Disorders journal, Jessica Heron, a research fellow in Birmingham University's mental health research team, claims that a quarter of women who experience mild euphoria after childbirth go on to develop postnatal depression within two months.
She followed 500 women from their 12-week antenatal scan to eight weeks after they had their babies.
Her findings are backed by the responses of more than 1000 mothers asked about postnatal depression by the parenting website Mumsnet. Of those who responded, 48 per cent said they were not diagnosed for up to a year.
A further 13 per cent suffered for between a year and 18 months before their condition was identified. Almost 40 per cent of women said they received no treatment.
NEED HELP?
A New Zealand website set up by the Postnatal Depression Family/Whanau New Zealand Trust gives information and advice on where to get help.
mothersmatter.co.nz
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