Reproductive and menstrual factors and risk of peritoneal and ovarian endometriosis.

Objective Between 1987 and 1989 data were collected to evaluate risk factors for pelvic endometriosis. Design A case-control study was conducted on 241 cases with laparoscopically or laparotomically confirmed peritoneal or ovarian endometriosis consecutively admitted to three teaching hospitals in Northern Italy. The control group consisted of 437 women admitted to hospitals for acute conditions covering similar catchment areas. Results Compared with nulliparous women, the risk of endometriosis decreased with increasing number of births: the point estimates were 0.4 and 0.3, respectively, for those with one and two or more births (X 2 1 trend=50.3, P Conclusions This study found that parity and irregular/long menses lower the risk of endometriosis. These findings were similar in different subgroups of disease location and indication for surgery, giving strong evidence of the consistency of the general results.