Characteristics of first pregnancy in relation to early breast cancer. A case-control study.

We examined some characteristics of first pregnancy in 314 female breast cancer patients whose disease was diagnosed at < 45 years of age and who were identified through a population-based cancer registry in New York State and in 314 control women identified through birth records. Preeclampsia was reported less frequently on the birth records of the first recorded pregnancy in the cases than in those of the controls, with a relative risk of 0.28 (0.05 < p < 0.10, from logistic model). We examined this finding on preeclampsia with particular reference to immunologic mechanisms, but further studies are needed on larger samples. Twinning and maternal Rh factor, also relevant to immunologic factors, were not significantly associated with a higher risk of breast cancer. Among the women whose first pregnancy resulted in a live birth, length of gestation (which is correlated with maternal estriol levels) did not differ between the cases and controls.