NEW YORK (Reuters Health) – The risk of sudden infant death syndrome (SIDS) is elevated in infants with parents who have been hospitalised for psychiatric illness or substance-abuse disorders, according to a new study.

Dr. Roger T. Webb, at the University of Manchester in England, and associates obtained information on single infant births, infant mortality, and adult psychiatric hospitalisations from national registries in Denmark. The researchers identified all cases of SIDS that occurred between 1973 and 1998.

In SIDS, which occurs without warning, apparently healthy infants seem to just stop breathing. The cause is unknown and most cases occur between the ages of two and four months.

In families with a parental history of psychiatric hospitalisation, either fathers or mothers, the risk of SIDS was roughly doubled compared with the frequency seen in the general population, the authors report in the Archives of General Psychiatry. If both parents were hospitalized, the risk of SIDS was increased by nearly seven-fold.

For specific disorders, the greatest risk was associated with inpatient treatment for substance abuse. The risk was especially high if mothers were hospitalised, which increased the risk by five-fold.

For mood disorders, such as depression, the risk was increased by about two-fold for hospitalisation of the mother or father.

Contrary to previous reports, schizophrenia-like disorders did not increase the risk of SIDS more than other psychiatric disorders.

"When treating severe adult psychiatric illnesses, it is important to identify patients who already have or will soon have infants in their care," Webb's group writes. "To help raise parental awareness of modifiable risk factors, these especially vulnerable infants may be better protected if infants' paediatricians are informed of parents' mental illnesses."