Development of spontaneous endometriosis in baboons

Objective: To determine the incidence of spontaneous endometriosis over a 32-month period in baboons with initially normal pelves. Methods: In this observational longitudinal study, which was performed at the Institute of Primate Research, Nairobi (Kenya), 24 baboons with laparoscopically confirmed normal pelves underwent 67 serial laparoscopies (mean 2.8 +/- 1.9, median 3, range 1-6) after 1-3 months (n = 8), 4-6 months (n = 11), 7-9 months (n = 9), 10-12 months (n = 17), 13-15 months (n = 6), 16-18 months (n = 4), 19-21 months (n = 3), 22-24 months (n = 4), 25-27 months (n = 1), and 30-32 months (n = 4). During each laparoscopy, the pelvis was examined for the presence of endometriosis. The number, size, and type of endometriotic implants were noted on a pelvic map, and the endometriosis score and stage were tabulated according to the revised classification of the American Fertility Society. Taking into account the variable length of follow-up, we used life-table analysis to calculate the cumulative incidence of endometriosis. Results: The cumulative incidence of minimal endometriosis (proven by histology) was 64% up to 32 months of follow-up. The eight baboons that developed proven endometriosis were followed over longer periods of time and had undergone more laparoscopies than the animals that did not develop the condition. Conclusion: There is a high incidence of minimal endometriosis in baboons, which increases with the time of follow-up and the number of repeat laparoscopies.