Adverse effects of endometriosis on pregnancy

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Endometriosis is an independent risk factor for developing placenta previa, according to a case-control study. The Japanese investigators also found that patients with a history of surgical treatment for endometriosis before pregnancy were more likely to develop the complication.

“This may be due to the more severe stage of endometriosis found in these patients,” the authors wrote in the journal BMC Pregnancy and Childbirth. Conversely, patients who had received only hormone therapies or who were coincidentally diagnosed with ovarian endometriosis in the first trimester of pregnancy were not at greater risk.

Methods
This study comprised 2,769 patients who gave birth at Nagoya University Hospital between 2010 and 2017. Maternal and neonatal outcomes were compared between women with endometriosis (n = 80) and without endometriosis (n = 2,689).

The endometriosis group was divided into two groups: surgical treatment (patients with a history of surgical treatment, including cystectomy for ovarian endometriosis, ablation or excision of endometriotic implants, and adhesiolysis) (n = 49) and nonsurgical treatment (those treated with only medications or without any treatment) (n = 31).

Findings
A univariate analysis concluded that placenta previa and postpartum hemorrhage were significantly more prevalent in the endometriosis group compared to the control group (those without endometriosis): 12.5% vs. 4.1% (P <  0.01) and 27.5% vs. 18.2% (P = 0.04), respectively. Endometriosis also significantly increased the likelihood of placenta previa in a multivariate analysis: adjusted odds ratio (OR) = 3.19; 95% confidence interval [CI]: 1.56 to 6.50 (P < 0.01). But this connection did not hold true for postpartum hemorrhage in the multivariate analysis: adjusted OR = 1.14; 95% CI: 0.66 to 1.98 (P = 0.64).

An additional analysis to identify patients with a high risk for placenta previa in the endometriosis group found that patients in the surgical treatment group were at higher risk for placenta previa than the nonsurgical treatment group: crude OR = 4.62; 95% CI: 2.11 to 10.10 (P < 0.01)

In particular, patients with a lapse of greater than 5 years between pregnancy and a previous surgery had a higher likelihood of placenta previa: crude OR = 5.92; 95% CI: 1.65 to 21.30 (P < 0.01). Other maternal and neonatal outcomes were comparable between the two groups.

Conclusions
Study findings are consistent with previous studies that found a link between endometriosis and placenta previa, according to the current authors. But the underlying mechanisms associating endometriosis with pregnancy complications remain mostly unclear. Several published papers indicate that chronic inflammation, adhesions, progesterone-resistant endometrium and a vascularized environment due to endometriosis might lead to various complications during pregnancy.

For placenta previa, one hypothesis is that hyperperistalsis of the uterus may cause abnormal blastocyst implantation, whereas dense pelvic adhesions could inhibit the migration of the placenta away from the internal ostium of uterus. The increased risk of placenta previa in patients with endometriosis who under surgery prior to pregnancy may be due to a higher rate of severe stage of endometriosis or a recurrence of the condition. Also, additional adhesions from operative manipulation might play some pathological role in placenta previa.

Because the majority of patients with endometriosis in the nonsurgical treatment group were treated conservatively, they could have had a milder variety of endometriosis compared to patients in the surgical treatment group.

Limitations
One limitation of the study is that diagnosis of endometriosis in the nonsurgical treatment group was gleaned from ultrasound, magnetic resonance imaging, and patient symptoms, which are less reliable than the gold standard, laparoscopy. The authors said additional studies are needed to investigate the connection between the site and stage of endometriosis or the method of surgical treatment and placenta previa in a subsequent pregnancy.