Human Teratogens and Evidence-based Teratogen Risk Counseling: The Motherisk ApproachNAVA-OCAMPO, ALEJANDRO A. MD; KOREN, GIDEON MDClinical Obstetrics & Gynecology: March 2007 - Volume 50 - Issue 1 - pp 123-131 doi: 10.1097/GRF.0b013e31802f1880 First Trimester Pregnancy Complications Abstract Author Information There are only a limited number of drugs proven to be human teratogens including thalidomide, isotretinoin, coumarin derivates, valproic acid, and folate antagonists. In some cases, the combination of 2 drugs may increase the teratogenic risk. The risk of birth defects may also vary with the time at which the drug is administered during pregnancy and the dose. There are some examples of drugs in which the dose has proven to be a major determinant of their teratogenicity in humans. There is more safety information for older than for newer drugs. Proactive teratogen risk counseling should include a critical appraisal of all available data including the consequences of the untreated maternal condition. The Motherisk Program, Division of Clinical Pharmacology and Toxicology, The Hospital for Sick Children, Toronto, Canada Correspondence: Gideon Koren, MD, The Motherisk Program, The Hospital for Sick Children, 555 University Avenue, Toronto ON M5G 1X8, Canada. E-mail: firstname.lastname@example.org © 2007 Lippincott Williams & Wilkins, Inc.