French researchers examined 181 mothers, and found that three-quarters of the 9% suffering severe depression had delivered a male child.
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: “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.”
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.
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.
The researchers did not have any evidence of a reason behind this difference, and called for further research to discover it.
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.”