MedWire News: The type of antipsychotic drug a pregnant woman is taking may influence the birth weight of her baby, UK research indicates.

"The available data are insufficient to justify wholesale changes in prescribing recommendations but do point to the need for careful monitoring of foetal growth in pregnant women prescribed atypical antipsychotics," the researchers comment.

'Typical' antipsychotic drugs represent the older generation of drugs, and include medications such as thioridazine, flupentixol and sulpiride. The newer, 'atypical' drugs include olanzapine and amisulpiride.

Dr. R Hamish McAllister-Williams, from Royal Victoria Infirmary in Newcastle upon Tyne, and colleagues found that 20% of babies born to 25 mothers who took 'atypical' antipsychotic drugs during pregnancy were large for their gestational age.

This compared with 3% of babies born to 45 mothers who were taking 'typical' antipsychotic drugs and 2% of babies born to 38 mothers who were not taking antipsychotics.

"These preliminary findings suggest that the risk of weight gain seen in patients treated with atypical antipsychotics may also occur to infants exposed in utero," say the researchers.

More babies born to mothers who took typical antipsychotic drugs were small for gestational age, at 16% compared with 0% of those whose mothers took no drugs. But this difference was substantially reduced by accounting for the mothers' use of weight-altering therapies.

The researchers stress that doctors should not consider switching pregnant women from a typical to an atypical antipsychotic drug to prevent their babies from being underweight, however.

Besides the unknown risks to the developing foetus, there is also the danger of destabilising the mother's illness by switching treatments, they note.