Background: The presence of uterine endometrial polyps is associated with not only abnormal uterine bleeding but also infertility, so the use of hysteroscopic polypectomy has been increasing. This operation is considered to increase cost-effectiveness when performed prior to infertility treatments. However, there are typical problems to consider, including the possibility of spontaneous regression of the polyp and the duration of complete endometrial wound healing after surgery. Meaningless interventions must be avoided, when possible. Therefore, data acquisition and analysis of various findings obtained from surgery have become important for improving treatment procedures and patient selection. To estimate the spontaneous regression rates and contributions of multiple factors to uterine endometrial polyps during the waiting period (approximately 2-3 months) before hysteroscopic polypectomy, we performed a multivariate analysis of data from the records in our hospital. Methods: The medical records of 450 cases from September 2014 to April 2021 in our hospital were retrospectively reviewed under the approval of our Institutional Review Board. We included all cases of hysteroscopic polypectomy with postoperative pathological diagnosis. We defined cases as having a "spontaneously regressed polyp" when the target polyp was not detected by postoperative pathological examination. We extracted data on the following ten factors:"Advanced age" (>= 42 years),"Small polyp" (< 10 mm),"High body mass index" (>= 25 kg/m(2)),"Nulliparity,""Single polyp,""Infertility,""Hypermenorrhea,""Abnormal bleeding,""No symptom," and "Hormonal drug use."We also classified cases into five groups according to the size of the polyp (<= 4.9 mm, 5.0-9.9 mm, 10.0-14.9 mm, 15.0-19.9 mm, and >= 20.0 mm) and determined the frequency of spontaneously regressed polyp in each group. Results: After exclusion of cases with insufficient data or other diseases, such as submucosal leiomyoma, 424 cases were analyzed. Among them, 28 spontaneously regressed polyps were identified, and the highest frequency of spontaneously regressed polyp was detected among the cases with polyps measuring 5.0-9.9 mm (16.4%). On multivariate analysis of the ten factors,"Small polyp" and "Hormonal drug use" were found to significantly impact the frequency of spontaneously regressed polyp. Conclusions: On the basis of the factors identified in this analysis, the indications for observation or medical therapy adapted to small polyps might be expanded.
