Summary
Teratogens—drugs, maternal conditions, substances, and environmental exposures—can cause congenital anomalies, growth restriction, or fetal death, especially during the first trimester. Risks include neural, cardiac, craniofacial, and limb defects, as well as neurodevelopmental impairments. Prevention relies on careful maternal management and avoidance of harmful exposures.
Introduction
Teratogens are environmental agents capable of causing permanent structural or functional abnormalities, growth restriction, or death in the developing embryo or fetus. The risk and type of teratogenic effects depend on the pharmacological properties, dose, timing of exposure, and maternal health factors.
Drugs and Teratogenicity
- Certain medications are strongly associated with congenital malformations.
Common Teratogenic Drugs and Associated Effects
|
Drug |
Teratogenic Effect |
|
Sodium valproate |
Neural tube defects (NTD), hypospadias, epicanthal folds, lip anomalies |
|
Carbamazepine |
NTD, posterior cleft palate, microcephaly |
|
Phenobarbital |
Cardiac malformations |
|
Phenytoin |
Cleft palate, microcephaly, hypoplastic phalanges |
|
Alcohol |
Growth retardation, intellectual disability |
|
ACE inhibitors |
Hypospadias, fetal loss, growth retardation |
|
Lithium |
Fetal goiter, cardiac anomalies |
|
Antithyroid drugs |
Fetal goiter, hypothyroidism |
|
Indomethacin |
Premature closure of ductus arteriosus |
|
Isotretinoin |
Craniofacial, heart, CNS anomalies |
|
Tetracycline |
Tooth discoloration |
|
Warfarin |
Nasal, eye, hand defects, growth retardation |
|
Androgens |
Virilization, esophageal and cardiac defects |
- Note: Diethylstilbestrol (DES) was banned due to its carcinogenic and teratogenic effects.
Timing and Mechanisms of Teratogenesis
- Teratogenic risk varies with the developmental stage of pregnancy.
Stages of Teratogenic Vulnerability
|
Phase |
Timing |
Significance |
|
Preimplantation |
0–15 days |
“All-or-nothing” effect; exposure may lead to spontaneous abortion |
|
Embryonic |
First trimester |
Organogenesis; highest risk for structural malformations |
|
Fetal |
Second and third trimesters |
Growth and functional maturation; may cause deficits in organ function, intellect, behavior, or minor structural anomalies |
Maternal Conditions and Teratogenic Risks
Maternal health significantly influences fetal development:
|
Maternal Condition |
Associated Fetal Effects |
|
Diabetes mellitus |
Diabetic embryopathy, fetopathy; cardiac defects, growth abnormalities |
|
Obesity |
Preterm birth, stillbirth, NTD, congenital heart disease, cleft lip/palate, macrosomia |
|
Graves disease |
Neonatal hyperthyroidism, growth restriction, preterm birth |
|
Hypothyroidism |
Congenital hypothyroidism, intellectual and developmental deficits |
|
Maternal PKU |
Intrauterine growth restriction, microcephaly, congenital heart disease, intellectual disability |
Substance Use and Teratogenesis
- Substance exposure during pregnancy contributes to structural and functional anomalies.
Substance-Related Fetal Risks
|
Substance |
Mechanism |
Effects |
|
Alcohol |
Impaired neuronal/glial migration |
Fetal alcohol syndrome: dysmorphic features, heart defects, holoprosencephaly, intellectual disability |
|
Tobacco |
Nicotine-induced vasoconstriction; CO hypoxia |
IUGR, low birth weight, preterm labor, ADHD, SIDS, cleft lip/palate |
|
Opioids |
Altered neurotransmitter levels |
Respiratory depression, neonatal abstinence syndrome, growth restriction, placental abruption |
|
Cocaine |
Vasoconstriction of uteroplacental vessels |
IUGR, low birth weight, preterm labor, placental abruption |
Physical and Chemical Teratogens
- Radiation: X-rays, CT, and nuclear medicine may cause microcephaly, intellectual disability, growth restriction, and malignancy.
- Metal Toxicity:
-
Lead: Spontaneous abortion, stillbirth, congenital anomalies.
-
Mercury: Cerebellar and cortical atrophy, polyneuritis.
-
Congenital Cardiac Defects
- Maternal conditions, infections, genetic syndromes, and teratogenic exposures are linked to congenital cardiac anomalies.
Conditions Associated with Congenital Cardiac Defects
|
Condition |
Cardiac Defects |
|
Maternal diabetes |
Transposition of great vessels, VSD |
|
Congenital rubella |
PDA, pulmonary artery stenosis, VSD, ASD |
|
Alcohol (FAS) |
VSD, PDA, ASD, Tetralogy of Fallot |
|
Prenatal lithium |
Ebstein anomaly |
|
Down syndrome |
ASD, VSD, AV septal defect |
|
Marfan syndrome |
MVP, thoracic aortic aneurysm/dissection, aortic regurgitation |
|
Turner syndrome |
Bicuspid aortic valve, coarctation of aorta |
|
Williams syndrome |
Supravalvular aortic stenosis |
|
22q11.2 microdeletion (DiGeorge) |
Truncus arteriosus, Tetralogy of Fallot |
Classic Teratogenic Syndromes
-
VACTERL association: Vertebral, anal, cardiac, tracheoesophageal, renal, limb anomalies.
-
Limb anomalies: Syndactyly, polydactyly, oligodactyly, ectromelia, phocomelia.
-
Thalidomide embryopathy: Amelia, micromelia, phocomelia, anotia.
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