A new study profiling the mothers who commit neonaticide, found the number of newborns in France killed within 24 hours of birth is at least five times higher than official statistics suggest.
Murder of newborns made headlines worldwide earlier this year when a French woman, Dominique Cottrez, admitted to killing eight of her offspring.
This and other cases raised questions as to how rare the practice was.
Anne Tursz and Jon Cook of the National Institute of Health and Medical Research near Paris examined court records in 26 judicial districts in France for 1996 to 2000, covering a third of all births during that period in metropolitan France.
The number of cases of neonaticide -- the murder of infants within a day of being born -- corresponded to a rate of 2.1 per 100,000 births, or 5.4 times the official rate of 0.39 cases per 100,000 births. Over the five-year period, the study uncovered 27 cases in the regions examined.
Even this new tally "is certainly vastly under-estimated," Turz told AFP.
"It must be on the order of about 100 [deaths] per year," with most of the bodies never found, she added.
Previous calculations of neonaticide were based on death certificates, not police and court records.
The researchers also sketched out a psychological and social profile of the 27 murderous mothers, nine of whom went missing.
The average age of the women was 26. A third already had at least three children, and more than half lived with the father of the newborn killed.
About two-thirds were employed, and the group as a whole did not differ significantly from other women in terms of social level or occupation.
Psychologically, most of the women were described as lacking confidence, immature and moody, and highly dependent on others.
None were clinically diagnosed as mentally ill.
"These were women starved of affection, faced with a terrible morale solitude," said Turz.
All of the women hid their pregnancies from their families and friends, though none were said be suffering from "pregnancy denial," a rare -- and disputed -- condition whereby women do not admit to themselves that they are carrying a child.
The mothers also gave birth alone and in secret.
"Identifying the profiles of the mothers will make it easier to identify vulnerable women so that appropriate solutions can be proposed," said Tursz.
"The findings suggest that preventative action targeting only the young, the poor, and women living alone, without work or in pregnancy denial, is misguided."
In another case from last year a French woman was found guilty of killing three of her newborns, keeping two of the bodies in her freezer and burning the third.
The study was published in the online edition of Archives of Disease in Childhood, a journal of the British Medical Association.
An earlier study by the same researchers, published in 2005, also showed that homicides of infants under one year old have also been seriously underestimated.