Maternal-placental-fetal unit: unique problems of pharmacologic study.

Fetal exposure to different drugs has increased, but few prospective, controlled, blinded trials have been conducted of adverse fetal effects following fetal drug exposure. The quantitative exposure of the fetus to drugs varies during pregnancy with changes in the MPFU. Prospective, controlled, blinded studies of adverse fetal effects of drugs are very difficult; investigators therefore have used alternative study designs that make the conclusions more tentative. Such studies may be limited by accuracy of recall of drug intake and its timing, oversimplification of complex drug exposure, separating the effects of drugs from that of the underlying disease, and a lack of correlation between human and animal effects of fetal drug exposure. Intentional drug treatment of the fetus has begun but should proceed from thorough laboratory study to clinical applications, not the reverse.