Prenatal adverse effects of various drugs and chemicals. A review of substances of frequent concern to mothers in the community.

Using the number of calls to the Canadian Motherisk Program as an indicator of the drugs and chemicals frequently of concern to mothers during pregnancy, the risks to the fetus of exposure to these compounds have been reviewed. The drugs which were of concern, and have been proven to be teratogenic, included alcohol, alkylating and antimetabolite agents, stilboestrol, disulfiram, heparin, lithium carbonate, phenytoin, tretinoin (retinoic acid), troxidone and valproic acid. For other compounds studied, there was either no data in the literature or no clear evidence of teratogenicity. The combination of doxylamine and pyridoxine, for example, has been associated with limb reduction defects in isolated case reports: cohort and case-control studies have failed to show a higher-than-baseline risk of malformations. In some cases of exposure to compounds with no known teratogenic potential, other adverse effects to the fetus are possible, and these effects are discussed in detail. In conclusion, when advising a pregnant woman about the potential teratogenic effect of a particular drug or chemical exposure, the health professional should also discuss other factors such as age, obstetric and medical history and the history of other exposures (including alcohol and smoking). In every pregnancy there is a 1 to 5% risk of mayor malformations, and even if the exposure does not appear to increase the teratogenic risk, such a risk still exists.