Is slight bleeding before menstruation associated with endometriosis?

This paper studied the association between premenstrual spotting and endometriosis in infertile women.

Endometriosis occurs when endometrial tissue (tissue that lines the inside of the uterus) grows outside of the uterus, causing pain and infertility. Currently, diagnosis of endometriosis is through visual inspection and biopsy (taking a sample of tissue from the body and examining it) obtained through laproscopy (surgery which makes a small incision to examine the body). However, laparoscopy is invasive, expensive and can lead to delayed diagnosis. Hence, it is important to discover a new diagnostic test for endometriosis. 

This study evaluated whether premenstrual spotting (small amount of bleeding before menstruation) can predict the diagnosis of endometriosis in women with infertility. 

Women who underwent laparoscopy for infertility were analyzed. After laparoscopy, biopsies were performed and analyzed for endometriosis. Patients also filled out a questionnaire regarding their infertility.

Of 80 patients, 38 women reported premenstrual spotting of 2 days and more and 42 women did not report premenstrual spotting. In women who did not report premenstrual spotting, 26% were diagnosed with endometriosis at laparoscopy. All these cases were staged as minimal (least severe).

Of women with premenstrual spotting, 89% were found to have endometriosis. Of these women with premenstrual spotting and endometriosis, 85% had advanced stage disease (quite severe). The ability of premenstrual spotting to predict presence of endometriosis was as good as that of  dysmenorrhea (pain during menstruation). When other factors were considered, women with premenstrual spotting were 16 times more at risk of endometriosis than women without premenstrual spotting. Premenstrual spotting of 2 days and more was associated strongly with red vesicular lesional phenotype (type of endometriosis). 

The authors concluded that premenstrual spotting of 2 or more days in women with infertility was strongly associated with endometriosis. 

If you are experiencing premenstrual spotting and are concerned, please talk to your doctor.