Image from the NCI publication "An Atlas of Findings of Human Females: After Intrauterine Exposure to DES". The cervix or cervix uteri is the lower part of the uterus in the human female reproductive system. Diethylstilbestrol (DES) is a synthetic nonsteroidal estrogen that was first synthesized in 1938. It is also classified as an endocrine disruptor. Human exposure to DES occurred through diverse sources, such as dietary ingestion from supplemented cattle feed and medical treatment for certain conditions, including breast and prostate cancers. From about 1940 to 1971, DES was given to pregnant women in the mistaken belief 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 drug in utero. The United States Food and Drug Administration subsequently withdrew DES from use in 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. The United States National Cancer Institute recommends women born to mothers who took DES undergo special medical exams on a regular basis to screen for complications as a result of the drug.