In the United States, approximately 3 percent of infants have a major structural malformation that is detectable at birth. By age 5, another 3 percent have been diagnosed with a malformation, and another 8 to 10 percent are discovered to have one or more functional or developmental abnormalities by age 18. For most birth defects—approximately 65 percent, the etiology is unknown (Schardein, 2000). Importantly, chemically induced birth defects, which include those caused by medications, are believed to account for less than 1 percent of all birth defects (Center for Drug Evaluation and Research, 2005). Selected examples of confirmed teratogens are listed in Table 14-1.
Table 14-1. Selected Drugs or Substances Suspected or Proven to Be Human Teratogens |Favorite Table|Download (.pdf)
Table 14-1. Selected Drugs or Substances Suspected or Proven to Be Human Teratogens
Angiotensin-converting enzyme inhibitors and angiotensin-receptor blockers
Medications are commonly prescribed for pregnant women, and in France, Lacroix and colleagues (2000) found this to average 13.6 medications. Nearly all drugs in pregnancy are used off-label because of the paucity of research and clinical trials. The study of medication use in pregnancy is hampered at least in part by the difficulty of studying this special population given the vulnerability of the developing fetus. In addition, there are numerous physiological changes in pregnancy such as alterations in blood volume, plasma proteins, and gastric emptying and transit time that affect dosing and distribution of drugs.
A teratogen is any agent—chemicals, viruses, environmental agents, physical factors, and drugs—that acts during embryonic or fetal development to produce a permanent alteration of form or function. The word teratogen is derived from the Greek teratos, meaning monster. A hadegen—after Hades, the god who possessed a helmet conferring invisibility—is an agent that interferes with normal maturation and function of an organ. A trophogen is an agent that alters growth. Hadegens and trophogens generally affect processes occurring after organogenesis or even after birth. Chemical or physical exposures that act as hadegens or trophogens are much harder to document. For simplification, most authors use the word teratogen to refer to all three types of agents.
Evaluation of Potential Teratogens
A birth defect in a newborn exposed prenatally to a certain drug, chemical, or environmental agent arouses concern that the agent is a teratogen. The two approaches used currently to identify teratogenicity after a drug is released for clinical use include follow-up studies and case-control surveillance (Mitchell, 2003). Before such culpability is established, specific criteria that follow the tenets in Table 14-2 must be considered:
- The defect must be completely characterized....