Parity in relation to mortality and cancer incidence: a prospective study of Norwegian women

Few prospective studies relating childbearing to total and cause-specific mortality and cancer incidence have been published. The purpose of this paper was to examine these relations in a large cohort of Norwegian women.

Information on reproductive factors was obtained through interviews with 63,090 women. All deaths and cancer cases during follow-up, 1961-1980, were obtained by linkage to the files at the Central Bureau of Statistics and the Cancer Registry of Norway, respectively. Associations with parity were assessed by stratified logistic regression.

For cerebrovascular and ischaemic heart disease, moderate but highly significant positive trends of increasing mortality with increasing parity were observed in the older part of the cohort. Deaths from diseases of the respiratory system and suicide were most common among nulliparous women. Inverse associations with parity were observed for cancers of the breast, corpus uteri and ovaries as well as for melanoma and non-melanoma skin cancers. Positive associations were observed for cancer of the cervix uteri in all age groups, for cancer of the respiratory system among older women and for pancreatic cancer and multiple myelomas in the younger part of the cohort. The results gave no support to previous reports of positive associations with cancer of the liver or gallbladder.

The study supports evidence of an increased risk of ischaemic heart disease in multiparous women, which had been observed previously in three smaller prospective studies. It confirms earlier observations of low risks of cancer of the breast, corpus uteri and ovaries in women with high parity.