Natural History and Risk Factors for Adverse Outcomes of Ovarian Endometrioma in Pregnancy — A 9-Year Cohort with Histopathological Confirmation

Mengyao Luo, Quanting Tao, Jing WangDepartment of Obstetrics, Hangzhou Women’s Hospital, Hangzhou, Zhejiang, People’s Republic of ChinaCorrespondence: Jing Wang, Department of Obstetrics, Hangzhou Women’s Hospital, Hangzhou, Zhejiang, People’s Republic of China, Email [email protected]: This study aimed to characterize the natural history of ovarian endometrioma (OE) during pregnancy and identify independent risk factors for adverse outcomes.Patients and Methods: This retrospective cohort study was conducted at Hangzhou Women’s Hospital and included 151 patients with OE histopathologically confirmed during cesarean section between January 2017 and December 2025. Patients were stratified according to the timing of OE detection: Group 1 (n = 86; OE detected before conception or before 14 weeks of gestation) and Group 2 (n = 65; OE first identified intraoperatively during cesarean section). The serial cyst dimensions in Group 1 were reviewed to assess gestational changes in cyst size during pregnancy. Composite adverse outcomes included cyst rupture, suspected malignant transformation, or cyst-related iatrogenic preterm birth. Risk factors were evaluated using univariable and multivariable logistic regression analyses.Results: Among 151 patients (median age, 31 years [IQR, 29– 34 years]), cyst behavior in Group 1 was heterogeneous: 17.4% decreased, 60.5% remained stable, and 22.1% increased in size. Revised American Society for Reproductive Medicine (rASRM) stage III–IV disease (61.6%) was significantly more prevalent in Group 1 (80.2% vs 36.9%; P < 0.001). Cyst rupture occurred in 20 patients (13.2%), decidualization in 26 (17.2%), and composite adverse outcomes in 22 (14.6%). rASRM stage III–IV disease (aOR = 5.784; 95% CI: 1.549– 21.596; P = 0.009) and decidualization (aOR = 4.530; 95% CI: 1.541– 13.316; P = 0.006) were independent risk factors for adverse outcomes, whereas absolute cyst size was not.Conclusion: The gestational course of OE is characterized by considerable interindividual variability; most cysts remain stable, whereas approximately one-fifth enlarge. rASRM stage III–IV disease and decidualization were independent risk factors for adverse outcomes, whereas cyst size alone was not. Increased surveillance may be warranted for patients with advanced-stage disease or sonographic features suggestive of decidualization.Keywords: pregnancy, ovarian endometrioma, decidualization, adverse outcomes, rASRM stage