Long-term impact of reproductive factors on the risk of cervical, endometrial, ovarian and breast cancer.

The influence of maternal age, parity, low or high birthweight, multiple births, and pre-eclampsia on the risk of cervical, endometrial, ovarian and breast cancers was studied. Data on 40951 women and the outcomes of their deliveries between 1955 and 1995 were obtained from birth registers. For the mothers, data from the Swedish Cancer Registry and the Cause of Death Register were added. The sample was evaluated using Cox's regression in univariate and bivariate analyses where the relative risk and its 95% confidence interval were calculated. Increasing maternal age at first birth was associated with an increasing relative risk of endometrial, ovarian, and breast cancers, and with a decreased risk of cervical cancer. Multiparity was a protective factor for all gynaecological cancers, including cervical and breast cancers. Multiple births were associated with an increased risk of endometrial cancer.