Which teratogenic agent is known to cause limb malformations in developing fetuses?

The teratogenic agent known to cause limb malformations in developing fetuses is thalidomide. Originally introduced as a sedative and later used to treat morning sickness in pregnant women during the late 1950s and early 1960s, thalidomide was found to cause severe birth defects, particularly affecting the limbs. Infants born to mothers who took thalidomide during pregnancy were born with phocomelia, a condition characterized by short or absent limbs.

Thalidomide's effects on limb development occur due to its influence on angiogenesis and limb morphogenesis during the critical periods of fetal development. Other teratogenic agents also exist, but thalidomide is particularly notorious for its association with limb malformations. Efforts to regulate and understand the risks of such drugs have since led to stricter guidelines for pharmaceutical use during pregnancy.