Types of Agents Resulting in Teratogenesis or Adverse Outcomes
Infectious: Agents in this category include bacteria (e.g., chlamydia and gonorrhea cause neo-natal eye and ear infections), viral (e.g., rubella, cytomegalovirus, herpes virus), spirochetes (e.g., syphilis), or protozoa (e.g., toxoplasmosis).
Ionizing radiation: No single diagnostic procedure results in radiation exposure to a degree thatwould threaten the developing pre-embryo, embryo, or fetus. No increase is seen in fetal anoma-lies or pregnancy losses with exposure of <5 rads. The greatest risk of exposure is between 8 and 15 weeks’ gestation with the risk a nonthreshold, linear function at doses of at least 20 rads.
Chemotherapy: Risk is predominantly a first-trimester phenomenon. Second- and third-trimester fetuses are remarkably resistant to chemotherapeutic agents.
Environmental: Tobacco is associated with intrauterine growth restriction (IUGR) and pre-term delivery, but no specific syndrome. Alcohol is associated with fetal alcohol syndrome: midfacial hypoplasia, microcephaly, mental retardation, and IUGR.
Recreational drugs: Cocaine is associated with placental abruption, preterm delivery, intraven-tricular hemorrhage, and IUGR. Marijuana is associated with preterm delivery but not with any syndrome.
Medications: These agents account for 1–2% of congenital malformations. The ability of a drugto cross the placenta to the fetus depends on molecular weight, ionic charge, lipid solubility, and protein binding. Drugs are listed by the FDA as category A, B, C, D, and X.
FDA Categories of Drugs
• Category A—Controlled studies show no risk. Adequate studies show no risk to thefetus in any pregnancy trimester. This includes acetaminophen, thyroxine, folic acid, and magnesium sulfate.
• Category B—No evidence of risk in animals but human studies have not been done. This includes penicillins, cephalosporins, methyldopa, insulin, Pepcid, Reglan,Tagamet, Vistaril, Paxil, Prozac, Benadryl, and Dramamine.
• Category C—Risk cannot be ruled out. Risk is present in animals but controlled stud-ies are lacking in humans. This includes codeine, Decadron, methadone, Bactrim, Cipro, AZT, b-blockers, Prilosec, heparin, Protamine, Thorazine, Alupent, Robitussin, and Sudafed.
• Category D—Positive evidence of risk. Studies demonstrate fetal risk, but potentialbenefits of the drug may outweigh the risk. This includes aspirin, Valium, tetracycline, Dilantin, Depakote, and Lithium.
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• Category X—Contraindicated in pregnancy. Studies demonstrate fetal risk, whichoutweighs any possible benefit. This includes Accutane (isotretinoin), Danocrine, Pravachol, Coumadin, and Cafergot.
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Specific Syndromes
Alcohol. Fetal alcohol syndrome—IUGR, midfacial hypoplasia, developmental delay, shortpalpebral fissures, long philtrum, multiple joint anomalies, cardiac defects.
Diethylstilbestrol. DES syndrome—T-shaped uterus, vaginal adenosis (with predisposition to vaginal clear cell carcinoma), cervical hood, incompetent cervix, preterm delivery.
Dilantin. Fetal hydantoin syndrome—IUGR, craniofacial dysmorphism (epicanthal folds,depressed nasal bridge, oral clefts), mental retardation, microcephaly, nail hypoplasia, heart defects.
Isotretinoin (Accutane). Congenital deafness, microtia, CNS defects, congenital heart defects.
Lithium. Ebstein’s anomaly (right heart defect).
Streptomycin. VIII nerve damage, hearing loss.
Tetracycline. After fourth month, deciduous teeth discoloration.
Thalidomide. Phocomelia, limb reduction defects, ear/nasal anomalies, cardiac defects,pyloric or duodenal stenosis.
Trimethadione. Facial dysmorphism (short upturned nose, slanted eyebrows), cardiac defects,
IUGR, mental retardation.
Valproic acid (Depakote). Neural tube defects (spina bifida), cleft lip, renal defects.
Warfarin (Coumadin). Chondrodysplasia (stippled epiphysis), microcephaly, mental retarda-tion, optic atrophy.
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