Background:
A woman’s risk of developing endometrial cancer (EC) decreases as her parity increases however the effects of grand multiparity (>5 full-term births), incomplete pregnancies and other birth outcomes are less clear.
Aims:
To assess risk of EC in relation to pregnancy outcomes.
Methods:
We conducted a meta-analysis with individual-level data from 29 studies (10 cohort, 19 case-control) in the Epidemiology of Endometrial Cancer Consortium including 16958 women with endometrial cancer and 39457 controls. Odds ratios (OR) and 95% confidence intervals (CI) were estimated from mixed-effects logistic regression considering study as a random effect, adjusted for potential confounders including age, parity, body-mass index (BMI), smoking and oral contraceptive (OC) use.
Results:
Preliminary analyses show the risk of EC decreases by 16% (OR=0.84, 95%CI 0.83-0.85) per full-term pregnancy, with progressive reductions in risk seen for up to seven full-term pregnancies (OR=0.22, 95%CI 0.18-0.28 vs. nulliparous women). This association was stronger among women aged <50 and for type 1 cancers, but did not differ by BMI or OC use. Risk also decreased by 7% per incomplete pregnancy, with a slightly stronger association seen among parous women (adjusted-OR=0.93, 95%CI 0.90-0.95) than nulliparous women (adjusted-OR=0.94, 0.87-1.02). We did not find any association between stillbirths, twinning and sex of offspring and endometrial cancer risk.
Conclusion: Full-term pregnancy is associated with a 16% reduction in EC risk, with benefits seen up to seven births. An independent and more modest reduction in risk is seen for incomplete pregnancies. Other pregnancy-related characteristics do not appear to influence risk.