Pharmacology of drug transfer across the placenta.

The effect of drugs in the fetus can be thought of in terms of the dose-response based on a knowledge of the general principles by which drug is transferred from the mother to the fetus. Fetal drug concentration, which determines the fetal response, is a function of the maternal concentration, the placental permeability, the fetal drug clearance, and differences in protein binding and ionization between the maternal and fetal plasma.