DES was discovered in 1938 and introduced for medical use in 1939. From about 1940 to 1971, the medication was given to pregnant women in the incorrect belief that it would reduce the risk of pregnancy complications and losses. In 1971, DES was shown to cause clear-cell carcinoma, a rare vaginal tumor, in girls and women who had been exposed to this medication "in utero". The United States Food and Drug Administration subsequently withdrew approval of DES as a treatment for pregnant women. Follow-up studies have indicated that DES also has the potential to cause a variety of significant adverse medical complications during the lifetimes of those exposed.