Teratology is the branch of medical science which studies the contribution of the environment to abnormal prenatal growth as well as morphological or functional developmental defects. Despite some pioneering research, the clinical and scientific interest in clinical teratology only developed because of the rubella pandemics in 1941 and the thalidomide tragedy in the late 1950s. The following decades have seen a definition of criteria for proof of human teratogenicity, the classification of drugs used in pregnancy, and the development of the “Teratogen Information Services” in developed countries.
Teratogens are chemical, physical or infectious agents, or a maternal status/disease whose prenatal exposure during the pregnancy can provoke developmental defects. Susceptibility to teratogenic agents depends on the combination of several factors, including the genotype of the mother and/or of the fetus, dosage, the gestational period at exposure, pharmacokinetics and the pharmacodynamic of the substance.
The methodology for the identification of teratogens includes animal studies, prospective epidemiologic studies and retrospective epidemiologic studies. The criteria for “proof” of human teratogenicity have not been defined although some criteria have been proposed and applied in the clinical/animal/epidemiologic studies. At present, some international classifications of drugs used in pregnancy are