A synthetic, nonsteroidal estrogen that was prescribed to many women until the early 1970s. It was thought to prevent or treat problems with pregnancy. However, female fetuses that were exposed to DES developed serious problems in their reproductive organs when they became adults. About 1/4th of exposed women develop anatomical problems with their cervix or vagina. Examples of these are underdeveloped cervix, small uterine cavities and abnormal fallopian tubes. These women are also more likely to have ectopic pregnancy, preterm labor, miscarriage and incompetent cervix. Women whose mothers took DES during pregnancy should mention this fact to their obstetrician so that potential problems can be identified and treated.