Fetal Damage Caused by Drugs
Certain medications taken during pregnancy can cause fetal damage, leading to congenital anomalies, developmental disorders, or even fetal death.
FDA Pregnancy Categories
Category A
- Definition: Studies in pregnant women have not shown an increased risk of fetal abnormalities.
- Examples:
- Folic acid
- Levothyroxine
Category B
- Definition:
- Animal studies have not demonstrated a risk to the fetus, but there are no adequate and well-controlled studies in pregnant women, OR
- Animal studies have shown an adverse effect, but adequate studies in pregnant women have not shown a risk.
- Examples:
- Amoxicillin
- Metformin
Category C
- Definition: Animal studies have shown an adverse effect on the fetus, and there are no adequate and well-controlled studies in humans. However, potential benefits may warrant the use of the drug in pregnant women despite potential risks.
- Examples:
- Tramadol
- Gabapentin
Category D
- Definition: There is positive evidence of human fetal risk based on adverse reaction data. However, potential benefits may warrant use in pregnant women despite the risks.
- Examples:
- Warfarin
- Lithium
Warfarin
- Effects:
- Nasal hypoplasia
- Stippled epiphyses
- Limb hypoplasia
- CNS abnormalities
- Eye defects
Mechanism:
- Inhibits vitamin K-dependent clotting factors.
- Interferes with bone and cartilage development.
- Disrupts normal embryologic signaling, particularly affecting craniofacial and skeletal structures.
Lithium
- Effects:
- Ebstein's anomaly (atrialized right ventricle)
- Hypothyroidism
- Neonatal goiter
Mechanism:
- Alters thyroid and parathyroid hormone regulation.
- Disrupts normal cardiac and endocrine development during organogenesis.
Category X
- Definition: Studies in animals or humans have shown fetal abnormalities, and the risks
outweigh any possible benefit. These drugs are contraindicated in pregnancy.
- Examples:
- Isotretinoin
- Thalidomide
Thalidomide
- Effects:
- Phocomelia (seal-like limb deformities)
- Cardiac defects
- GI malformations
Mechanism:
- Inhibits angiogenesis.
- Disrupts limb bud development during early embryogenesis.
- Impairs mesodermal growth and signaling.
- Usage: Originally used in the 1950s–60s as a sedative and for morning sickness.
Isotretinoin (Accutane)
- Effects:
- Craniofacial abnormalities (e.g., micrognathia, cleft palate)
- Cardiovascular defects
- CNS malformations (e.g., hydrocephalus)
- Thymic hypoplasia
Mechanism:
- Affects gene expression related to cell proliferation, differentiation, and apoptosis.
- Disrupts neural crest cell migration.
- Strong teratogen during the first trimester (critical organogenesis period).
- Usage: Used for severe nodulocystic acne.
- Contraindications: Requires strict pregnancy prevention program (e.g., iPLEDGE).