A teratogen is a compound which permanently deforms the function or structure of a developing fetus in utero. In general, the degree of teratogenicity depends on:
- potency of the drug as a mutagen;
- susceptibility of the fetus to teratogenesis;
- dose of the teratogen;
- duration of teratogen exposure;
- degree of transfer from maternal to fetal circulation; and
- point during gestation at which teratogen exposure occurred.
Two to three percent of all live births are complicated by malformation. The majority of these complications are due to unknown factors. The vast majority of recognized etiologies are genetic, with only 10% being attributed to environmental etiologies such as maternal health, infection, and teratogenesis. In general, the central nervous system, ears, eyes, and limbs are the most affected.
Women may encounter a number of teratogens. Smoking is most likely to cause growth retardation, but has also been implicated in prelabor rupture of the membranes, preterm labor, abruption of the placenta, spontaneous abortion, perinatal morbidity and mortality, and sudden infant death syndrome. Smoking likely exerts its effects through competitive binding of carbon monoxide with hemoglobin, and peripheral vasoconstriction leading to fetal hypoxia.
Alcohol use in pregnancy may result in Fetal Alcohol Syndrome (FAS). FAS occurs in approximately 1% of all births. FAS children present with a flattened upper lip, thin upper lip, small palpebral fissures, epicanthal folds, flattened nasal bridge, short nose, and may also exhibit microcephaly, mental retardation, and have learning disabilities. It is not clear if there is any safe amount of alcohol consumption in pregnancy .
Cocaine generally produces growth restriction, preterm delivery, microcephaly, spontaneous abortion, placental abruption, limb anomalies, and central nervous system abnormalities. Cocaine likely exerts its effects through peripheral vasoconstriction leading to fetal hypoxia.
Women with indications for warfarin therapy should either abstain from pregnancy or switch to low molecular weight heparins. Warfarin typically produces mental retardation, growth restriction, nasal hypoplasia, and opthalmic abnormalities.
Angiotensin Converting Enzyme (ACE) inhibitors will cause fetal renal failure and oligohydramnios which lead to pulmonary hypoplasia and limb contracture. Fetal cranial bone abnormalities are also common.
Isotretinoin (Accutane), used to treat acne, may cause cardiac, otological, thymic, and central nervous system abnormalities. In one quarter of cases, it causes mental retardation.