Although rare, the true incidence of neonaticides - the unlawful killing of a baby within the first 24 hours of its life - is more than five times as common as official estimates suggest, suggests research published online in the Fetal and Neonatal edition of the Archives of Disease in Childhood.

Low maternal self esteem and emotional immaturity, rather than obvious mental illness or social disadvantage, are key drivers, the research indicates.

The researchers reviewed the case records of 26 courts in three regions of France, involving the death of a child within the first day of life between 1996 and 2000, and which came to trial between 1996 and 2007. The analysis included the psychiatric assessment of the mothers.

Among 80 cases of intentional violent deaths during this period, a third (27 cases) were unlawful killings during the first day of life. The authors reviewed the records of all cases and analysed the characteristics of the 17 cases where the mother had been identified.

There was a "sizeable underestimate" in official statistics of neonaticides. The official statistics put the figure of the unlawful killing of newborns at 0.39 per 100,000 births for the same regions over the same period.

But the court data point to 2.1 per 100,000, equal to a rate that is actually five times higher.

When the authors analysed the mothers' profiles, they found that the perception of a young poor, unemployed, single woman as the culprit was not borne out by the evidence.

The judicial data showed that the average age of women who unlawfully killed their babies was 26. One in three had at least three children already. Two thirds had not used contraception while the rest used it irregularly for this particular pregnancy.

More than half lived with the dead child's father and two thirds were employed in jobs similar to those of women in the general population.

None of the women seemed to be obviously mentally ill, nor had there been any clear denial of the pregnancy - factors often said to be associated with these cases. No history of the mother having been abused as a child had been recorded either.

But all the pregnancies had been concealed from family and friends. No deliveries took place in medical facilities, and all but three of the 17 women gave birth secretly and alone. Almost half the women were depressed.

What distinguished them were their low levels of self esteem, emotional immaturity, dependency on others, and fear of being abandoned by them.

"Feeling very much alone, and for nearly half of them, depressed, [these women] probably did not have complete control over their lives or their sexuality," say the authors. "Neonaticide thus appears as a solution when an unwanted pregnancy risks creating a family scandal, or the loss of one's partner or a satisfying lifestyle," they continue.

"Our findings suggest that preventive action, targeting only young, poor, unemployed and single women, or women in pregnancy denial, may not be appropriate," they add.