Which drug taken by a pregnant woman shows a delayed teratogenic effect in the offspring, making the effect difficult to identify?

Diethylstilbestrol

Explanation:

Diethylstilbestrol (DES) is a synthetic form of the female hormone estrogen. It was prescribed to pregnant women between 1940 and 1971 to prevent miscarriage, premature labor, and related complications of pregnancy. DES is now known to be an endocrine-disrupting chemical, one of a number of substances that interfere with the endocrine system to cause cancer, birth defects, and other developmental abnormalities. The effects of endocrine-disrupting chemicals are most severe when exposure occurs during fetal development.