Endometriosis increases odds of pregnancy loss

Endometriosis was associated with greater odds of pregnancy loss and recurrent pregnancy loss, according to a Danish nationwide cohort study published in Fertility and Sterility.

Endometriosis and a subtype of endometriosis, adenomyosis, are associated with changes in fertility and pregnancy outcomes, according to study background.

“Current studies, including a wide-ranging meta-analysis, found an association between endometriosis and pregnancy loss, while other studies did not find an association,” Amalie Dyhrberg Boje, MD, who was a medical student in the department of OB/GYN at Copenhagen University Hospital Hvidovre, Denmark, at the time of the study, and colleagues wrote. “The studies had different aims and did not differentiate between the numbers of pregnancy losses. To our knowledge, this is the first study of its kind to investigate the association between endometriosis and pregnancy losses making a distinction between the number of pregnancy losses.”

Defining the cohort

Boje and colleagues used data from the Danish National Health Register to identify women born between 1977 and 1997 who did and did not have a diagnosis of endometriosis by 2017. Women with endometriosis were aged-matched 1:10 with women who did not have endometriosis.

The researchers also examined Danish Medical Birth Register data through 2017 to identify the individual-level number of pregnancy losses, which were defined as spontaneous terminations of pregnancy before 22 weeks’ gestation.

In total, 29,563 women with endometriosis and 295,630 women without endometriosis were included in the cohort. Women with endometriosis more commonly conceived with assisted reproductive technology compared with their counterparts (14.1% vs. 4.4%), as well as had fewer pregnancies and parities.

Of note, 5,863 (19.8%) women with endometriosis and 51,753 (17.5%) women without endometriosis had never been pregnant.

Findings

Among women who had ever been pregnant, 23,700 (80.2%) women with endometriosis and 243,877 (82.5%) women without endometriosis had experienced pregnancy loss at least once.

Compared with women who did not have endometriosis, women with endometriosis were more likely to have experienced one (OR = 1.13; 95% CI, 1.09-1.17), two (OR = 1.18; 95% CI, 1.1-1.26) or three or more (OR = 1.44; 95% CI, 1.31-1.59) pregnancy losses. Adjusting for gravidity, women with endometriosis were more likely to have experienced one (adjusted OR = 1.37; 95% CI, 1.32-1.42), two (aOR = 1.75; 95% CI, 1.62-1.89) and three or more (aOR = 2.57; 95% CI, 2.31-2.85) pregnancy losses.

Additionally, women with endometriosis had greater odds of the following types of recurrent pregnancy loss vs. women without endometriosis:

• primary (OR = 1.8; 95% CI, 1.54-2.1);
• secondary (OR = 1.3; 95% CI, 1.1-1.52);
• secondary after giving birth to a boy (OR = 1.41; 95% CI, 1.12-1.73);
• after a complicated delivery (OR = 1.57; 95% CI, 1.1-2.26); and
• at least three pregnancy losses before age 30 years (OR = 1.47; 95% CI, 1.26-1.71).

There were no associations between endometriosis and two or more pregnancy losses in the second trimester, stillbirth or secondary recurrent pregnancy loss after giving birth to a girl.

Notably, subgroup analyses of women with endometriosis and adenomyosis and with adenomyosis only revealed a stronger association between endometriosis and a greater number of pregnancy losses compared with women without endometriosis.

“Future studies should consider investigating pregnancy tissue from women with recurrent pregnancy loss with and without endometriosis to study the expression of local immune cytogenetic factors or inflammatory processes during pregnancy to explore potential pathophysiological associations in endometriosis and pregnancy losses,” Boje and colleagues wrote.