The risk of infertility associated with endometriosis may not be nearly as high as previously thought, according to results of a new study published in Human Reproduction.
Researchers at Brigham and Women’s Hospital looked at data collected from 58,427 premenopausal, married female nurses aged <40 years, from 1989 to 2005. The women were participants in the Nurses’ Health Study II prospective cohort. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated via multivariate Cox proportional hazards regression models.
In the cohort, they found 4612 incident cases of infertility due to any cause over the course of 362,219 person-years of follow up. When compared to women with no history of endometriosis, those with a history of the condition had an age-adjusted 2-fold increased risk of incident infertility (HR = 2.12, 95% CI = 1.76–2.56). This was attenuated after taking into account parity. A relationship between endometriosis and infertility was only seen among women aged < 35 years (multivariate HR <35 years = 1.77, 95% CI = 1.46–2.14; multivariate HR 35–39 years = 1.20, 95% CI = 0.94–1.53; P-interaction = 0.008). The risk of primary versus secondary infertility was similar following endometriosis diagnosis.
Among women who had primary infertility, 50% became parous after being diagnosed with endometriosis. Among all women with endometriosis, 83% were parous by age 40 years.
The investigators concluded that their results support a temporal link between infertility risk and endometriosis. They believe that the results also indicated a possible detection bias in previous studies examining endometriosis and infertility. They also concluded that the risk of infertility posed by endometriosis may be half what was seen in earlier cross-sectional analyses.