Oskari Heikinheimo explains link of endometriosis and higher risks of miscarriage, ectopic pregnancy

Individuals with surgically verified endometriosis face significantly higher risks of early pregnancy complications—including miscarriage and ectopic pregnancy—compared with those without the condition, according to a large registry-based cohort study published in American Journal of Obstetrics & Gynecology in January 2026. The findings add long-term, population-level evidence to a growing body of research examining how endometriosis affects reproductive outcomes well before and after diagnosis.

The study followed 10,105 individuals in Finland with a first surgical diagnosis of endometriosis between 1998 and 2012 and compared them with 19,526 age- and residence-matched controls. Using national registries, investigators captured all pregnancies occurring from age 15 through the end of follow-up, yielding more than 256,000 person-years in the endometriosis cohort and more than 503,000 person-years among controls. Overall, individuals with endometriosis had a lower lifetime incidence of pregnancy than those without the condition, with an adjusted incidence rate ratio of 0.87.

Among pregnancies with known outcomes, births were less common in the endometriosis cohort (72.0% vs 75.7%, respectively), whereas miscarriage (15.6% vs 10.4%) and ectopic pregnancy (3.5% vs 1.5%) were significantly more frequent. After adjustment, endometriosis was associated with a 51% higher risk of miscarriage and more than a 2-fold increased risk of ectopic pregnancy. By contrast, the risk of induced abortion was lower, and there was no difference in the risk of molar pregnancy.

“This is part of a longstanding research effort that we have been doing on endometriosis,” said Oskari Heikinheimo, Department of Obstetrics and Gynecology, Helsinki University Hospital and University of Helsinki. “Using the Finnish registries, we were able to look at deliveries, miscarriages, ectopic pregnancies, induced abortions, and molar pregnancies, and compare the rates of these outcomes in women with endometriosis vs control women.”

Heikinheimo emphasized that the most clinically important findings involved early pregnancy loss. “The most interesting and important finding was that the rate of ectopic pregnancy was significantly higher among endometriosis women, and similarly, the rate of miscarriage was significantly higher,” he said, noting that these complications were observed even before surgical diagnosis and in first pregnancies.

The study also found fewer induced abortions among individuals with endometriosis, a pattern Heikinheimo attributed in part to endometriosis management and family planning. “Since overall fertility is reduced among women with endometriosis, we think that there are fewer pregnancies which are not so planned,” he said.

Although the results do not support routine screening for early pregnancy complications, Heikinheimo said awareness is critical. “Being aware of this increased risk of ectopic pregnancy and miscarriage is important,” he said. “Not to frighten patients, but to inform care and counseling.” He added that the findings reinforce the value of timely diagnosis, which may allow patients to plan pregnancies and access reproductive support earlier.

Reference:

Gurney JM, Tuominen A, Saavalainen J, et al. Endometriosis and early pregnancy outcomes: a registry-based cohort study in Finland. Am J Obstet Gynecol. 2026 doi:10.1016/j.ajog.2026.01.027.