Among women with infertility, 25-50% have endometriosis

Endometriosis is associated with a higher risk of subsequent infertility, but only among women age <35 years. This study included data collected from 58 427 married premenopausal female nurses <40 years of age from 1989 to 2005, who are participants of the Nurses' Health Study II prospective cohort. Compared with women without a history of endometriosis, women with endometriosis had an age-adjusted 2-fold increased risk of incident infertility.

The study is targeting women with reproductive challenges. There is not control group since the diagnosis method is very invasive (laparoscopy). It seems there is a high proportion of cases with endometriosis but it could be bias to the selection of these patients by their doctors, and it is unclear the difference with a standard control group.