Boy babies increase the probability of severe postpartum depression.

French researchers examined 181 mothers, and found 9% had severe depression - three-quarters of these had delivered a male child.

The Journal of Clinical Nursing study suggested earlier poor relationships with men could be a factor for some.

However, a specialist in the UK said the finding, although interesting, could be a "statistical quirk".

“The overwhelming finding of the study was the fact that gender appears to play a significant role in reduced quality of life as well as an increased chance of severe postnatal depression “ Professor Claude de Tychey University of Nancy

Postnatal depression is common among new mothers - the latest study at the University of Nancy found a third of those taking part were affected to some degree.

In some societies, having a female baby has been linked to the condition - due to the cultural preference for a male child.

However, the idea that having a male baby could exacerbate the problem is an unexpected one.

The women involved were questioned on several different areas of their health, including physical fitness, pain and mental and emotional health.

The researchers, led by Professor Claude de Tychey, found that seven out of ten women who had given birth to a boy reported a lower quality of life compared with the average of women who had given birth to a girl, regardless of whether they had postnatal depression.

Although mothers of girl babies were more likely to have mild postnatal depression, among the 17 women diagnosed with severe postnatal depression, 13 had male babies.

Emotional difference

The researchers did not have any evidence of a reason behind this difference, and called for further research to discover it.

However, although they suggested there might be subtle psychological differences in the attitudes of new mothers towards boy and girl babies which might affect their emotional state - particularly if they were already prone to depression.

They suggested a negative attitude to a son might be a legacy of unsatisfactory relationships with important male figures in their life, such as their father, or partner.

Professor de Tychey said: "The overwhelming finding of the study was the fact that gender appears to play a significant role in reduced quality of life as well as an increased chance of severe postnatal depression. "Women had the same scores regardless of whether the recent birth was their first or second baby."

However, Dr Cosmo Hallstrom, a member of the Royal College of Psychiatrists, said the numbers of women with severe depression were too low to draw firm conclusions. He said severe depression results were compromised by the finding that a majority of the mothers with mild depression were more likely to have given birth to girls. "It's an interesting talking point, but I'm not entirely convinced by this, and would like to see it replicated in larger trials. It's probably a statistical quirk."