The infertility risk associated with endometriosis is about half that of previous estimates suggesting possible detection bias in previous studies, according to a new report published in Human Reproduction.

In the study, “A prospective cohort study of endometriosis and subsequent risk of infertility,” researchers at Brigham and Women’s Hospital used clinical information from 58,427 married premenopausal female nurses less than 40 years old who were enrolled in the Nurses’ Health Study II prospective cohort.

“Although women with endometriosis are at greater risk for infertility compared to women without endometriosis, our study suggests that the majority of women with endometriosis do not experience infertility and the majority do become pregnant and are able to build the families that they desire,” said senior study author Stacey A. Missmer, Sc.D, director of Epidemiologic Research in Reproductive Medicine at Brigham and Women’s Hospital, in a news release.

While endometriosis is frequently identified during an infertility diagnosis, a causal link to infertility has yet to be determined. Since surgical visualization (laparosopy) is the gold standard for a definitive diagnosis of the disease, prevalence and incidence estimates among infertile women is likely overestimated. It is possible that women with otherwise ‘asymptomatic’ endometriosis secondary to the primary causes of infertility are over-represented, and those women would not have received a laparoscopic diagnosis of endometriosis had they not attempted to become pregnant.

From the total data, researchers were able to identify 4,612 incident cases of infertility due to any cause over 36,2219 combined years of follow-up of the study participants. Compared to women without endometriosis, women with endometriosis were two times at increased risk of incident infertility.

The relationship with endometriosis was only observed among women less than 35 years of age. Risk of primary versus secondary infertility was the same following endometriosis diagnosis. Among women with primary infertility, 50% had given birth to a child after an endometriosis diagnosis, and among all women with endometriosis, 83% bore a child by age 40.

The results indicated that the infertility risk posed by endometriosis is about half previous estimates, which reveals a likely detection bias in earlier studies.

“A key step in endometriosis discovery is identifying women with endometriosis who indeed are at higher risk of infertility so that treatments can be targeted directly to the biology causing infertility and identifying these women as early as possible so they can access fertility treatment,” Missmer said.