DES (diethylstilbestrol) is a synthetic form of estrogen that was prescribed between 1940 and 1971 to help women with certain complications of pregnancy. Among other things, daughters of women who used DES during pregnancy are susceptible to a rare cancer of the vagina or cervix called clear cell adenocarcinoma—a cancer that is practically non-existent in non-exposed women in this age group . Because of this risk, DES daughters need a special exam at least once a year. DES daughters are also at an increased risk for infertility, having an increased incidence of structural changes in their reproductive organs, and may want to see a doctor experienced in treating DES-exposed women.

DES daughters also have a higher risk for ectopic pregnancy, miscarriage, and preterm labor and delivery. While most DES daughters can become pregnant and carry their babies to term, because of the above risks, all DES daughters require high-risk obstetric care and early confirmation of pregnancy. DES daughters should be seen more frequently throughout their pregnancies.

Women who used DES may have a slightly increased risk of breast cancer. Children and grandchildren of women who took DES during pregnancy are at an increased risk of developing significant injuries ranging from rare cancers to genital abnormalities.

Although less is known about the consequences of DES exposure in men than in women, a number of concerns have been identified. Some DES sons face an increased risk for problems with their genital organs. These range from harmless irregularities to problems, which may require medical treatment. Epididymal cysts are the most common abnormality in DES sons.

The epididymis is a structure on the back of each testicle where sperm is stored. Epididymal cysts are non-cancerous growths. They may disappear and recur over time. Testicular problems in some men exposed to DES include both small testicles and undescended testicles. Men with undescended testicles have an increased chance of developing testicular cancer, whether or not their mothers took DES. An abnormally small penis (microphallus) occurs more often in DES sons than in other men.

Some studies have indicated that testicular varicoceles occur more often in DES sons than in other men. A varicocele is an irregularly swollen or varicose vein on the testicle. This enlarged vein produces a higher temperature than is normal for testicles, and—over a period of years—can lower the number of normal sperm as a result. Hypospadias is a condition where the opening of the penis is located on the under-surface of the penis rather than at the end.

A 1995 study comparing a group of men exposed to DES to a group of men not exposed to DES found that DES had no effect on fertility. The men in this study were all born between 1950 and 1953. The study measured the following factors as indicators of fertility: whether the men had ever impregnated a woman, age at the birth of their first child, average number of children, medical diagnosis of a fertility problem, or length of time to conception in the most recent pregnancy of the female partner. This study indicates that DES does not seem to affect fertility in males.