Introduction -- The alert clinician -- Animal experiments and adverse drug reaction reports -- Some epidemiological principles -- Pregnancy outcomes with the exception of congenital malformations -- Congenital malformations -- Identification of maternal use of drugs -- The problem of confounding -- Statistics -- Lumping or splitting? Paternal use of drugs -- Timing of drug use and effects on the embryo or fetus -- Repeated studies and meta-analysis -- Pharmacovigilance -- Information on the risk with drug use during pregnancy -- Concluding remarks.