A combo platter of antiretrovirals and a common class of drugs for pneumocystis carinii pneumonia (PCP) taken during pregnancy may be hazardous to the fetus. In a study of 189 London moms-to-be, researchers discovered that women in their first trimester who were on both HAART and a so-called folate antagonist -- the class of drugs (including Bactrim) used to ward off PCP -- had a sevenfold increased risk of birth defects in offspring compared to HIVers who were drug free. The folate antagonists are known perps in folic-acid depletion, which is known to cause congenital abnormalities. But what has scientists scratching their heads is the finding that taking either HAART or the Bactrim-type meds alone in early pregnancy apparently posed no threat. The double was trouble.

If the British data are confirmed, it will have weighty implications for the therapeutic choices of mothers-to-be, especially those with fewer than 200 CD4s who are advised to take PCP prophylaxis. Meanwhile, docs recommend storing up on the B vitamin folic acid.