Does endometriosis affect miscarriage risk in IVF pregnancies?

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In women whose pregnancies are a result of in vitro fertilization (IVF), risk of miscarriage is not increased by endometriosis, according to results of a retrospective cohort study.

The findings are contrary to the belief that endometriosis negatively impacts the effectiveness of assisted reproductive technology (ART) by causing an increased risk of miscarriage. 

The Chinese study in the journal Reproductive Biology and Endocrinology enrolled women undergoing a first IVF cycle who had singleton pregnancies after fresh embryo transfer in a tertiary hospital reproductive medical center between January 2008 and June 2016. All were younger than age 42.

In total, 1,006 women with endometriosis were compared to 2,012 women with no endometriosis (control group), for a 1:2 ratio.

The miscarriage rate for the two groups was similar: 22.4% for the patients with endometriosis and 20.1% for those without the condition.

After adjustment for miscarriage risk factors (body mass index, parity, age, duration of infertility and male factor infertility), the odds ratio (OR) was 1.14 (95% CI 0.95 – 1.37).

The investigators also found no difference in risk of miscarriage between women with and without endometriosis: 19.8% and 23.8%, respectively (OR 0.79, CI 0.58 – 1.09).

The miscarriage rate in women with endometrioma ≥ 30 mm or < 30 mm was not significantly different either: 24.7% and 18.5%, respectively (OR 1.44, CI 0.79 – 2.63).

“After adjustment for risk factors for miscarriage, the presence of endometrioma and the size of endometrioma, regression model confirmed no significant increase for the risk of miscarriage in the subgroup analyses,” the authors wrote.

Some previous studies have indicated a strong association between age and higher risk of miscarriage, which was not the case in the current study.

Also, some studies advocate that endometriomas > 30 mm should be treated surgically before ART, whereas other studies assert that such surgery might seriously damage ovarian reserve and therefore compromise success. But the current study concluded that presence of endometrioma does not affect the miscarriage rate. 

Besides conflicting results among several studies, the mechanism of endometriosis-related infertility and its influence on poor IVF outcomes has yet to be fully established, according to the authors, who noted that the process of endometriosis could impact oocyte quality, quantity, and endometrial receptivity with inflammatory factors.

Two of the strengths of the current study are that the results were based on a large sample size and that the characteristics of endometriosis and the size of endometriomas were evaluated.

On the other hand, “it was not possible to find the exact surgical classification endometriosis in the analysis, since the women had surgery in different hospitals and these data were not available in the registry,” the authors wrote. Moreover, the sonographic diagnosis of ovarian endometrioma was not always very reliable.