Parity and coronary heart disease among women in the American Cancer Society CPS II population.

Four of five cohort studies have shown an increase in cardio-vascular disease with increased parity, after control for a number of cardiovascular risk factors. The effect has been observed primarily in categories of four or more livebirths. To analyze this issue further, we conducted an analysis of 585,445 women from the American Cancer Society Cancer Prevention Survey II (CPS II). There were 4,787 deaths from coronary heart disease (International Classification of Diseases Codes 410-414) among these women during the follow-up period from 1981 to 1989. After controlling for a number of cardiovascular risk factors, we found no increased trend in heart disease with increased parity. Rare ratios for women with no live births or 1, 2, 3, 4, 5, and 6 or more livebirths were 1.00, 0.95, 0.89, 0.82, 0.94, 0.98, 0.94, respectively. Without control over confounders, however, we observed an increased risk for the highest party category (rate ratio = 1.18; 95% confidence interval = 1.04-1.34). Positive findings for parity to date have been found primarily in cohort studies representative of the general population, whereas our own data and another earlier negative study among nurses came from more select populations likely to be relatively homogeneous for socioeconomic variables. Positive findings in the literature may be due, at least in part, to confounding by unmeasured variables related to socioeconomic status.