Is a long period without childbirth a risk factor for developing endometriosis?

Endometriosis was found in 42 (20%) of 206 symptom-free, parous Norwegian women with a mean age of 37 years at the time of sterilization. Case-control analysis between the 42 women with endometriosis and the 164 without endometriosis revealed an increased risk of endometriosis with increasing number of years since the last childbirth. After 10 years without a birth, the odds ratio for endometriosis was 4.5 compared with the first 5 years after the last delivery. An increased risk of endometriosis with increasing age of the women could not be detected. If these findings from women with voluntary infertility are transferred to women with endometriosis associated with involuntary infertility, endometriosis could be a consequence of a long period without childbirth. This might explain why endometriosis is often diagnosed in infertile women.