Decidualization of endometriosis in a cohort of IVF-mediated pregnancies

Decidualization is the process of endometrial change in pregnancy, a phenomenon that can involve also ovarian endometriomas. However, the frequency of this event remains unknown. In addition, there is no evidence on the decidualization of deep invasive endometriosis (DIE). To shed more light on this issue, we prospectively recruited women with ovarian endometriomas or DIE who underwent IVF. They were subsequently excluded if they did not become pregnant or if they had a miscarriage. The evaluation was repeated in five time points during pregnancy and post-partum. The primary outcome was the rate of decidualized endometriomas at 11–13 weeks’ gestation. Data from 45 endometriomas and 15 nodules were available for data analyses. At the 11–13 weeks’ ultrasound, endometriomas’ decidualization was observed in seven cases, corresponding to 16% (95% CI 8–29%). Subsequent assessments in pregnancy failed to identify any additional case. DIE also underwent significant changes during pregnancy. At the 11–13 weeks’ ultrasound, lesions were increased in size and more vascularized. In conclusion, decidualization of ovarian endometriomas in IVF pregnancies is not rare. DIE may also undergo decidualization, but further evidence is needed for a robust and shared definition of this process.