Endometriosis and Endometrial Polyps Co-Occurrence in Individuals Not Seeking Pregnancy: A Case-Control Study

Endometriosis and endometrial polyps are both estrogen-dependent conditions, and an association between these two pathologies has been observed in infertile women. Our research question was: "Is there an association between endometriosis and endometrial polyps also in a study population not selected for infertility?" Therefore, we aimed to assess whether the prevalence of endometrial polyps is higher in patients with endometriosis not seeking pregnancy compared with a general gynecologic outpatient population.

This is a case-control study including 438 women with endometriosis and 438 controls without endometriosis attending routine gynecologic visits, consecutively identified from the electronic health records of the Gynecology Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy.

Between November 2021 and July 2025, all participants underwent transvaginal ultrasound, with standardized pelvic/uterine assessment according to the IETA, IDEA, and MUSA criteria. Patients using hormonal therapy at the time of the examination or in the previous 2 months were excluded. The primary endpoint was the prevalence of endometrial polyps in the two study groups. Point estimates of proportions in each group and odds ratios were calculated with corresponding 95% confidence intervals. Multivariate logistic regression was used to calculate adjusted odds ratio.

The mean age was 32 (28-36) years in the 438 cases and 32 (26-36) years in the 438 controls (p = 0.13). Most participants were Caucasian, with a comparable distribution of ethnicities between the two study groups (89.3% and 87.2%; p = 0.23). Prior use of hormonal treatment was reported significantly more often by women with endometriosis (72% vs 48%; p < 0.001). Endometrial polyps were detected in 7/438 women with endometriosis (1.6%) and in 11/438 without endometriosis (2.5%; OR 0.63, 95% CI 0.24-1.64, p = 0.35). When both current and past diagnoses of endometrial polyps were considered, prevalence rates were 3.4% in cases and 5% in controls (OR 0.67, 95% CI 0.34-1.31, p = 0.24). Similar findings were observed after adjusting for statistical and clinically relevant variables.

Considering the unexpectedly small number of endometrial polyps detected, a type II error cannot be excluded. Moreover, a 2-month hormonal therapy washout period among previous users might have been too short to fully rule out a potentially persistent protective effect of medications on the development of endometrial polyps. A possible misclassification bias cannot be excluded as polyps were diagnosed by ultrasound without direct visualization by hysteroscopy and histologic confirmation. No centralized image review was performed, introducing potential inter-operator variability. Finally, as no individual matching between cases and controls was performed, residual confounding cannot be completely excluded despite statistical adjustment.

In women not seeking pregnancy, endometriosis was not associated with a higher prevalence of endometrial polyps compared with a general gynecologic population undergoing routine gynecologic visits. These findings suggest that the co-occurrence of endometriosis and endometrial polyps observed in infertile populations may reflect independent correlations of the two pathologies with a common determinant condition (infertility) rather than a true biological relationship between them.