Vaginal bleeding and diethylstilbestrol exposure during pregnancy: relationship to genital tract clear cell adenocarcinoma and vaginal adenosis in daughters.

Comparing 186 cancer cases and 1772 cancer-free controls and reexamining several previously published studies, we found genital tract clear cell adenocarcinoma and vaginal adenosis to be moderately, but nonsignificantly, associated with vaginal gestational bleeding when in utero diethylstilbestrol exposure was statistically controlled. Considering the prevalence of diethylstilbestrol exposure in the general population, the relative risks of vaginal clear cell adenocarcinoma for in utero exposure were 365.6 and 459.0 when vaginal bleeding did and did not occur during the index pregnancy, respectively. The relative risks of vaginal adenosis for such diethylstilbestrol exposure were 15.4 and 92.8, respectively, for these women. The strong associations between in utero diethylstilbestrol exposure and both vaginal adenosis and genital tract clear cell adenocarcinoma cannot be attributed to the occurrence of problem pregnancy. However, among daughters exposed to diethylstilbestrol, maternal vaginal bleeding during the index pregnancy does appear to be associated with reduced risks of vaginal adenosis and vaginal clear cell adenocarcinoma.