Discuss the effects of thalidomide on pregnant women.

Answers will vary. Thalidomide was marketed in the 1960s as a treatment for insomnia and nausea and provides a dramatic example of critical periods of vulnerability to teratogens. A fetus's extremities undergo rapid development during the second month of pregnancy. Thalidomide taken during this period almost invariably causes birth defects, such as missing or stunted limbs. The drug is no longer prescribed for pregnant women.