Increased prevalence and recurrence of retrograde menstruation in baboons with spontaneous endometriosis.

This study was done to test the hypothesis that the incidence and recurrence of retrograde menstruation is higher in baboons with spontaneous endometriosis than in those without. A total of 399 laparoscopies was performed on 113 female baboons. Group 1 consisted of 84 animals with a normal pelvis (including 23 that later underwent induction of endometriosis and were assigned to group 4), group 2 comprised nine baboons with spontaneous endometriosis acquired during the last 2 years of the study, group 3 had 18 baboons with long-term spontaneous disease, and group 4 comprised 25 animals with induced endometriosis. Retrograde menstruation was defined by the presence of blood-stained peritoneal fluid (red or dark brown) during menses. Recurrence of retrograde menstruation was analysed during the first two laparoscopies in 13 baboons. Peritoneal fluid was 10 times more frequently blood-stained during menses (62%) than during non-menstrual phases (6%). Retrograde menstruation was observed more frequently in animals with spontaneous disease (groups 2 and 3, 83%) than in animals with a normal pelvis (group 1, 51%). Recurrence of retrograde menstruation was observed more frequently in baboons with spontaneous endometriosis (5/5) than in those without (3/8). The results of this study demonstrate that retrograde menstruation is common in baboons, with a higher prevalence and recurrence in animals with spontaneous endometriosis than in those without.