Aim-To analyse the relationship between reproductive and menstrual factors and different stages of pelvic endometriosis.

Methods-Between 1987 and 1990 a case-control study of risk factors for pelvic endometriosis was conducted.

Cases comprised 376 women with pelvic endometriosis confirmed by laparoscopy or laparotomy admitted to any one of three clinics in Lombardy, northern Italy.

A total of 129 (34.3%) of these women were at stage 1,76 (20.2%) at stage 2,96 (25.5%) at stage 3, and 75 (19.9%) at stage 4, according to the American Fertility Society revised classification of endometriosis.

Controls comprised 522 women admitted to hospital for acute conditions.

Results

The risk of endometriosis decreased with increasing number of births.

The estimated odds ratios (OR) were similar in different stages of the disease : for example, compared with nulliparous women, the OR of endometriosis at stage 1 was 0.1 in women who reported two or more births and the corresponding values were respectively 0.1,0.2, and 0.2 for endometriosis at stages 2,3, and 4. Cases reported fewer induced abortions than controls : the estimated ORs compared with no induced abortion were 0.4,0.5,0.2, and 0.2 in women who reported one or more induced abortions for subsequent stages of endometriosis.

Women with irregular menstrual cycles were at less risk of the disease : compared with women who reported lifelong regular cycles the estimated ORs were 0.3,0.5,0.5, and 0.3 for disease stages 14 respectively.