Endometriosis is associated with an increased risk of adverse pregnancy outcomes such as ectopic pregnancy, gestational diabetes, and preterm birth, a large study has found.

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Leslie V. Farland, ScD, of the University of Arizona, Tucson, and coauthors reported their analysis of data from 196,722 pregnancies in 116,429 women aged 25-42 years enrolled in the Nurses Health Study II cohort in Obstetrics & Gynecology.

Among the women with eligible pregnancies, 4.5% had laparoscopically confirmed endometriosis. These women were found to have a 40% higher risk of spontaneous abortion than were women without endometriosis (19.3% vs. 12.3%) and a 46% higher risk of ectopic pregnancy (1.8% vs. 0.8%). The risk of ectopic pregnancy was even more pronounced in women without a history of infertility.

Researchers also saw a 16% higher risk of preterm birth in women with endometriosis (12% in women with endometriosis vs. 8.1% in women without endometriosis), and a 16% greater risk of low-birth-weight babies (5.6% in women with endometriosis vs. 3.6% in women without endometriosis).

There also was the suggestion of an increased risk of stillbirth, although the researchers said this finding should be interpreted with caution because of the small sample size.

Women with endometriosis also had a 35% greater risk of gestational diabetes than did women without endometriosis. This association was stronger in women younger than age 35 years, in women without a history of infertility, and in women undergoing their second or later pregnancy. Endometriosis also was associated with a 30% greater risk of hypertensive disorders of pregnancy, particularly in second or later pregnancies.

Dr. Farland and associates wrote that recent research on the relationship between endometriosis and pregnancy outcomes had yielded “mixed results.”

“For example, much of the research to date has been conducted among women attending infertility clinics, which may conflate the influence of advanced maternal age, fertility treatment, and infertility itself with endometriosis, given the known elevated risk of adverse pregnancy outcomes in this population,” they wrote.

They suggested that one possible mechanism for the association between endometriosis and adverse pregnancy outcomes was progesterone resistance, which was hypothesized to affect genes important for embryo implantation and therefore contribute to pregnancy loss. Another mechanism could be increased inflammation, which may increase the risk of preterm birth and abnormal placentation.

“Elucidating mechanisms of association and possible pathways for intervention or screening procedures will be critical to improve the health of women with endometriosis and their children,” they wrote.

Katrina Mark, MD, commented in an interview, “This study, which identifies an increased risk of adverse pregnancy outcomes in women with endometriosis, is an important step in improving reproductive success.

“Although some explanations for these findings were postulated by the researchers, the next step will be to study the underlying physiology that leads to these complications so that interventions can be offered to improve outcomes,” said Dr. Mark, who is an associate professor of obstetrics, gynecology & reproductive sciences at the University of Maryland School of Medicine. Dr. Mark, who is not a coauthor of the study, was asked to comment on the study’s merit.

The study was supported by grants from the National Institutes of Health. Daniela A. Carusi, MD, received funding from UpToDate; Andrew W. Horne, MB, ChB, PhD, declared European government grants funding and consultancies with the pharmaceutical sector unrelated to the present study; Jorge E. Chavarro, MD, and Stacey A. Missmer, ScD, declared institutional funding from the NIH, and Dr. Missmer also received institutional funding from other funding bodies, as well as consulting fees. Dr. Farland and the remaining coauthors had no relevant financial disclosures. Dr. Mark has no relevant financial disclosures.

SOURCE: Farland LV et al. Obstetr Gynecol. 2019. doi: 10.1097/AOG.0000000000003410.

Endometriosis is linked to adverse pregnancy outcomes