Which agent among the following is historically linked to teratogenic limb defects when used during pregnancy?

• A. Diethylstilbestrol
• B. Thalidomide
• C. Ethanol
• D. Antiepileptic drugs

Answer: (B)

Limb formation depends on precise growth and blood vessel development during early pregnancy. Thalidomide caused a famous pattern of limb defects, such as severely shortened or absent limbs (phocomelia), when taken by pregnant women in the late 1950s and early 1960s. Its impact is linked to anti-angiogenic effects that disrupted blood vessel formation in the developing limbs, halting growth and leading to the characteristic malformations. Although thalidomide is now used under strict safeguards, this history stands as the clearest example of a drug causing teratogenic limb defects. Other options have notable teratogenic risks, but their hallmark effects differ—for instance, DES is associated with genital tract anomalies and cancer risk later in life, alcohol exposure leads to fetal alcohol spectrum disorders, and many antiepileptic drugs raise risks like neural tube and other defects rather than limb-specific malformations.