Endometriosis, Severe Maternal Morbidity, and the Effect of Infertility: Population-Based Cohort Study

This population-based cohort evaluated the association between endometriosis and severe maternal morbidity (SMM), and the mediating effect of infertility and fertility treatment. Included were all singleton deliveries in Ontario between 2006 and 2014. Modified Poisson regression generated adjusted relative risks. Mediation analysis estimated the direct effect of endometriosis and indirect effect through infertility and mode of conception. 787 449 deliveries were included (19 099, 2.4% with endometriosis). SMM occurred in 29.0 per 1000 deliveries among women with endometriosis, in contrast to 18.2 per 1000 deliveries among those without endometriosis-corresponding to an adjusted relative risk of SMM of 1.43 (95% CI 1.31-1.56). Mediation analysis demonstrated that the effect of endometriosis on SMM was independent of infertility or fertility treatment. We conclude that SMM in women with endometriosis appears to be due to the disease itself and not to infertility or related treatments.