For several decades, researchers have tried to determine whether exposure to DES before birth (in the womb) affects a woman's ability to become pregnant. Two earlier studies provided conflicting results that may have occurred because the women were in their early childbearing years when the studies were conducted and because their fertility histories were incomplete. In this study, the average age was 42; so these women had had many more reproductive years than women included in the two earlier studies.

This study compared the reproductive history of 1,753 DES Daughters with the reproductive history of 1,050 women not exposed to DES. The researchers found that compared with unexposed women, a greater number of DES Daughters had never become pregnant. Similarly, a greater number of DES Daughters, compared with unexposed women, tried for a year or more to become pregnant without success. In addition, researchers found that the timing of DES exposure in the womb (the trimester(s) during which exposure to DES took place) had some effect on infertility rates.

Specifically, 24% of DES Daughters had never become pregnant compared with 18% of unexposed women. Most DES Daughters who never became pregnant had been exposed to DES during the first 9 weeks in the womb. This finding supports earlier research, which found that structural abnormalities that affect fertility (such as endometriosis, abnormalities of the fallopian tubes, and inadequate production of cervical mucus) were more common among women whose DES exposure occurred during their mothers' first trimester of pregnancy.

Despite problems with becoming pregnant, 76% of DES Daughters eventually became pregnant compared with 82% of unexposed women.

Citation: Palmer JR, Hatch EE, Rao RS, Kaufman RH, Herbst AL, et al. Infertility among women exposed prenatally to diethylstilbestrol. Am J Epidemiol 2001;154:316-21.