Cancers of female organs rare among women with 5+ children
Marianne Hinkula's dissertation Incidence of gynaecological cancers and overall and cause specific mortality of grand multiparous women in Finland presented in March 2006, was selected as best mortality and health related dissertation of the year in the field of population science. It includes five population-based studies in a cohort of 87,000 women with at least five children. Altogether 7,600 cancer diagnoses and 18,900 deaths were recorded.
The incidence of cancers of the breast (SIR 0.55, 95% CI 0.52–0.58), endometrium (0.57, 0.52–0.63) and ovaries (0.64, 0.55–0.73) was decreased, and that of cervical cancer (1.13, 0.98–1.29) increased. The increase in parity from five to eight increased the protection against breast and endometrial cancer, but not in ovarian 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 reduced risk of postmenopausal endometrial cancer.
The mortality of breast (SMR 0.64, 0.59–0.69), endometrial (0.68, 0.56–0.80), ovarian cancer (0.68, 0.60–0.75) as well as for dementia (0.80, 0.72–0.84) were decreased. The SMR of kidney cancer (1.38, 1.21–1.56), ischemic heart diseases (1.10, 1.08–1.13) and diabetes mellitus (1.42, 1.29–1.55) were increased. The overall mortality of women with 5+ children was 5% below and among women with 10+ children 1% above the national average.
The pregnancy specific hormonal milieu is discussed to be 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.