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Friends and family of Paula Gilfoyle found it impossible to believe that she could have committed suicide and experts said that it was very rare for a pregnant woman to kill herself.

This incredulity and horror may have helped drive police to look for another explanation — which only could have been murder; and her erring husband was the obvious candidate.

Peter Marzuk, a psychiatrist at Cornell University Medical College in New York, said: “It would be unusual for a woman at a very advanced stage of pregnancy to commit suicide”. Professor Marzuk has noted that a foetus creates serotonin, some of which may find its way to the mother’s brain. A higher level of serotonin reduces the risk of depression and impulsive behaviour. He suggested in the American Journal of Psychiatry that, even if a pregnant woman was depressed, the serotonin made her less likely to act on any suicidal impulses.

Lanny Berman, of the American Association of Suicidology, which promotes research and education, said that some factors could put expectant mothers in danger. “In general, pregnancy protects against suicide, as she who is pregnant is bonding with the child-to-be and is generally eager to be a mother – of course, this is not true of all pregnant women,” Dr Berman said. “Women with a personal or family history of depression, relationship or personal difficulties, unplanned pregnancy, previous miscarriage, pregnancy complications, or a history of emotional, physical or sexual abuse, may be more at risk.”

A study of England and Wales between 1973 and 1984 showed pregnant women to be 20 times less likely to commit suicide than other women.

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