Purpose: To estimate the net effect of oral contraceptives (OC) on potentially fatal nonreproductive outcomes and life expectancy based on current patterns of OC use.
Method: We developed a model to simulate a cohort of US women, starting at age 10 and continuing until death or age 100, using month-long cycles. All probabilities were stratified by age, race-ethnicity, and BRCA1/BRCA2 status where possible. Other-cause mortality was obtained from US mortality data. Population-based incidence and mortality for deep venous thrombosis, pulmonary embolism, stroke, and myocardial infarction were estimated based on hospital discharge data from the Nationwide Inpatient Sample. Incidence and conditional survival for cancers was derived from registries maintained by the CDC and National Cancer Institute. Probabilities of contraceptive method usage were derived from the National Survey of Family Growth. Parameters were defined as distributions based on the available data and the parameter type. Relative risk estimates for each outcome conditional on OC use were derived from a systematic review and random effects meta-analyses, and subsequently used to estimate incidence in users and nonusers. As an alternative model, we included time-dependence for duration of use and ovarian cancer, and time since last use for breast cancer. Relative risks were characterized as lognormal distributions, based on the estimated odds ratio and 95% confidence intervals from the meta-analyses. We performed a series of microsimuations, including a two-dimensional analysis consisting of an outer loop of 200 draws from the relative risk estimates, with 10,000 simulated subjects per draw.
Result: At the population level, OC use consistently resulted in decreases in both incidence and mortality from ovarian, colorectal, and endometrial cancer. Incidence of breast cancer, cervical cancer and vascular events was consistently increased, but cause-specific mortality did not increase as much for these events, possibly due to lower age-specific mortality. This resulted in a net increase in life expectancy of 1-2 months, with the magnitude of increase greater with the time-dependent model. Life expectancy was decreased (by 1 month or less) in less than 5% of simulations.
Conclusion: Current evidence suggests that the noncontraceptive effects of OCs likely result in modest net gains in life expectancy, which should be reassuring to women who are currently considering OCs as a contraceptive method.
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