Endometriosis phenotype and preterm birth


There is no association between endometriosis and preterm birth, according to a French study in JAMA Network Open.

The study also found that disease phenotype does not seem to change the result.1

Hence, monitoring the pregnancy beyond the normal protocols or shifting management strategies for women with endometriosis may not be necessary to prevent preterm birth, according to the authors.

“Given the limitations of previous retrospective studies, it is still unclear whether endometriosis has adverse implications for pregnancy outcomes,” they wrote.

The study was conducted at 7 maternity units in France from February 2016 to June 2018. Patients received healthcare for a single pregnancy, with follow-up before 22 weeks 0 days of gestation, along with delivery in any of the maternity units.

A total of 1351 women with a mean age of 32.9 years who had a singleton delivery after 22 weeks’ gestation were analyzed.

In all, 470 women were assigned to the endometriosis group, of whom 10.2% had isolated superficial peritoneal endometriosis (SUP); 17.7% had ovarian endometrioma, potentially associated with SUP; and 72.1% had deep endometriosis (DE), also perhaps linked to SUP.

The control group comprised 881 women who lacked a history of clinical symptoms of endometriosis before their current pregnancy.

The endometriosis group was more likely than the control group to have a history of myomectomy and operative hysteroscopy. The former group was also more often nulliparous with fewer cesarean deliveries, whereas the multiparous women in the group incurred fewer preterm births between 22 and 36 weeks’ gestation.

In addition, for current pregnancies, the women in the endometriosis group were more likely to have had a longer median conception delay and a greater requirement for ART to conceive.

The major outcome was a preterm birth between 22 weeks and 36 weeks/6 days of gestation, regardless of cause.

The rate of preterm deliveries prior to 37 weeks 0 days of gestation between the endometriosis group and the control group were similar: 7.2% vs 6.0%, respectively (P =0.38).

There was also no difference observed in the prevalence of spontaneous or induced preterm birth between the two groups.

However, the rates of gestational diabetes and small for gestational age were significantly higher in the endometriosis group than in the control group: 17.2% vs 13.1%, respectively (P =0.04), and 15.6% vs 8.8%, respectively (P < 0.001).

Likewise, the median birth weight was significantly lower in the endometriosis group compared to the control group: 3190 g vs 3310 g, respectively (P < 0.001).

After adjusting for confounding factors, endometriosis was not linked to preterm birth before 37 weeks’ gestation: adjusted odds ratio (aOR) = 1.07; 95% confidence interval (CI): 0.64 to 1.77.

The preterm birth rates were also similar for the three disease phenotypes: 6.2% for SUP, 7.2% for OMA and 7.4% for DE (P = 0.84).

Although the authors concluded that women with endometriosis were not at increased risk of preterm birth, these women were more prone to threatened preterm labor; thus the authors could not exclude a connection between endometriosis, uterine contractions and cervical changes.

Furthermore, the mislabeling of pregnancies among women with endometriosis as high risk might explain the association between endometriosis and hospitalization for threatened preterm labor, according to the authors.


  1. Marcellin L, Goffinet F, Azria E, et al. Association between endometriosis phenotype and preterm birth in France. JAMA Netw Open. Published online February 8, 2022.doi:10.1001/jamanetworkopen.2021.47788
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