This is obviously a senstive subject, but one that is emmotive and of interest for all new parents and is probably worth a read..

New research has shown that cot death babies lack a key brain chemical that regulates breathing, heart rate and sleep.

Scientists in the US discovered abnormal amounts of serotonin in brain tissue samples taken from 35 children who died from Sudden Infant Death Syndrome (SIDS).

Levels of the chemical were 26% lower in the infants than in babies who died unexpectedly for other reasons.

Serotonin is a neurotransmitter that helps cells in the brain transmit messages to one another. It has a number of functions and may be crucial to a baby's breathing. The discovery may help explain the link between cot death and babies sleeping face down.

The research, led by Dr Hannah Kinney from the Children's Hospital, Boston, is published in the Journal of the American Medical Association.

Dr Kinney said: "The baby looks normal during the day; there's nothing that would tell you that baby is going to die of SIDS that night.

"There's something about sleep that unmasks the defect, which we believe is in serotonin circuits: the baby experiences some kind of stress during sleep, such as re-breathing carbon dioxide in the face-down position or increased temperature from over-bundling, that cannot be compensated for by the defective brainstem circuits, and the baby then goes on to die."

The next step is to find out what causes abnormally low serotonin levels in the first place, say the researchers. Genetic variations may be one explanation now being investigated by members of Dr Kinney's team.