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Drug Effects on the Fetus and Breast-Fed Infant

A major dilemma facing anyone who prescribes, dispenses, or administers drugs to a woman of childbearing age is that the patient may be or may become pregnant. This dilemma is heightened by the realization that drugs can and do adversely effect the embryo, fetus, and newborn. Fortunately, most medicinal agents produce no measurable effect on the developing offspring and, thus, are relatively safe during pregnancy. Druginduced teratogenicity and toxicity are limited to a few therapeutic agents. Awareness of these agents can be an effective means of diminishing the anxiety of prescribing for a woman who is or may become pregnant. Communication of this information to the patient can also lessen the anxiety she may experience when she is taking the therapy. A second important consideration is knowledge of the background incidence of birth defects, their various causes, and the percentage of the total that are believed to be drug-induced. The incidence of congenital malformations among live births is approximately 5–6% after long-term followup. Approximately half of these are diagnosed shortly after birth. The causes of birth defects and the approximate percentage of each are single major mutant genes (15– 20%), chromosomal aberrations (5%), multifactorial (polygene–environmental factor interactions) (20%), environmental factors (maternal conditions and diseases, deformations, radiation, hyperthermia, chemicals, drugs) (10%), and unknown (up to 65%). The combined incidence of birth defects resulting from radiation, hyperthermia, chemicals, and drugs is thought to be less than 1% but has been estimated in the past to be as high as 3%. Teratogen-induced congenital anomalies usually involve a combination of minor and major malformations. Underreporting of adverse outcomes is most likely common, therefore, because most drug-induced malformations are characterized by a pattern of minor anomalies rather than a single major defect. Part of the reason for this discrepancy is that the diagnosis of minor malformations is very difficult unless exposed offspring are studied in a systematic fashion with standardized physical examinations. Moreover, the long-term effects of drugs on neurobehavior are rarely studied. Henceforth, the terms “birth defects,” “anomalies,” or “congenital malformations” will be Correspondence: Gerald G. Briggs, B Pharm, 9802 Saline Drive, Huntington Beach, CA 92646 CLINICAL OBSTETRICS AND GYNECOLOGY Volume 45, Number 1, 6–21 © 2002, Lippincott Williams & Wilkins, Inc.