Background: Epidemiologic studies are consistent in finding that women who have had at least one birth are less likely to develop endometrial cancer. Less clear is whether timing of pregnancies during reproductive life influences risk, and the degree to which incomplete pregnancies are associated with a reduced risk.
Methods: We evaluated pregnancy history in relation to endometrial cancer risk using data from a series of 4 population-based endometrial cancer case-control studies of women 45–74 years of age (1712 cases and 2134 controls) during 1985–2005 in western Washington State. Pregnancy history and information on other potential risk factors were collected by in-person interviews.
Results: Older age at first birth was associated with a reduced risk of endometrial cancer after adjustment for number of births and age at last birth (test for trend P = 0.004). The odds ratio comparing women at least 35 years of age at their first birth with those younger than 20 years was 0.34 (95% confidence interval = 0.14–0.84). Age at last birth was not associated with risk after adjustment for number of births and age at first birth (test for trend P = 0.830). Overall, a history of incomplete pregnancies was not associated with endometrial cancer risk to any appreciable degree.
Conclusions: In this study, older age at first birth was more strongly associated with endometrial cancer risk than was older age at last birth. To date, there remains some uncertainty in the literature on this issue.
From the aDepartment of Epidemiology, School of Public Health, University of Washington, Seattle, WA; bDivision of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA; cDepartment of Internal Medicine, School of Medicine, University of New Mexico, Albuquerque, NM; dDepartment of Otolaryngology-Head and Neck Surgery, School of Medicine, University of Washington, Seattle, WA; and eUniversity of Wisconsin School of Medicine and Public Health, Madison, WI.
Submitted 19 January 2011; accepted 29 March 2011; posted 20 June 2011.
Supported by the National Cancer Institute (R35 CA39779, R01 CA47749, R01 CA75977, K05 CA92002, R01 CA105212, R01 CA87538) and the National Institute of Child Health and Human Development (N01 HD 2 3166), National Institutes of Health.
Correspondence: Gaia Pocobelli, University of Washington Department of Epidemiology, Box 357236, Seattle, WA 98195. E-mail: firstname.lastname@example.org.