Abstract

The aim of this population-based cohort study was to evaluate the incidence and relative risk ratios of gynaecological cancers and the mortality of women with at least five children (GM women) compared to the average of Finnish women. We linked together the data of the Population Register (1974–1997), the Finnish Cancer Registry and the national cause-of death files of Statistics Finland (1974–2001) by using a personal identification code. The study population consisted of 86 978 GM women (1974–1997), including 3 752 women with at least 10 children (GGM women). Altogether 7 604 cancer diagnoses and 18 870 deaths were recorded.

The incidence (SIR) of breast (0.55, 95% CI 0.52–0.58), endometrial (0.57, 95% CI 0.52–0.63) and ovarian cancer (0.64, 95% CI 0.55–0.73) decreased, and that of cervical cancer (1.13, 95% CI 0.98–1.29) increased in GM women. In multivariate analysis, the increase in parity from five to eight increased the protection against breast and endometrial cancer, but not in ovarian or cervical cancer. A young age at first birth decreased the breast cancer risk, while an older age at first birth decreased the risk for endometrial and cervical cancer. A short premenopausal delivery-free period and a long birth period were risk reducers in women who contracted endometrial cancer after menopause.

The mortality (SMR) of breast (0.64, 95% CI 0.59–0.69), endometrial (0.68, 95% CI 0.56–0.80), ovarian cancer (0.68, 95% CI 0.60–0.75) as well as for dementia (0.80, 95% CI 0.72–0.84) decreased. The SMR of kidney (1.38, 95% CI 1.21–1.56) cancer increased in the GM group. The SMR of ischemic heart diseases (1.10, 95% CI 1.08–1.13) and diabetes mellitus (1.42, 95% CI 1.29–1.55) increased. The overall SMR of GM women was 5% less than expected (95% CI 0.94–0.95; deficit 949 deaths), but among GGM women it coincided with the national average (1.01, 95% CI 0.93–1.08).

Multiparity affected the spectrum of diseases and causes of death in a specific way: the pregnancy-specific hormonal milieu is responsible for the low SIR and SMR of hormone-dependent cancers, and increased body weight is lightly responsible for the high SMR of cardiovascular and metabolic diseases. These observations advocate for delivering the first child at an age younger than 30 years and to start measures for careful weight control not only during and after pregnancies but even later and permanently.