Ping Hu ^1,2 Mengyue Chen ^1,3 Lu Zhu ¹ Bing Song ² Chao Wang ³ Yunxia Cao ^1,2* Xiaojin He ^1,4* Guanjian Li ^1,2*

• ¹ Reproductive Medicine Center, Department of Obstetrics and Gynecology, First Affiliated Hospital of Anhui Medical University, Hefei, Anhui,, China
• ² NHC Key Laboratory of Study on Abnormal Gametes and Reproductive Tract, First Affiliated Hospital of Anhui Medical University, Hefei, Anhui, China
• ³ Key Laboratory of Population Health Across Life Cycle, Ministry of Education of the People’s Republic of China, Hefei, Anhui Province, China
• ⁴ Reproductive Medicine Center, Shanghai General Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China

Introduction: Chronic endometritis (CE) is a prolonged, mild inflammation of the endometrial lining. This study investigated the impact of the impact of antibiotic treatment combined with vaginal Lactobacillus on pregnancy outcomes in infertile patients with CE during frozen embryo transfer (FET) cycles. Methods: A retrospective analysis was performed on the clinical data of 7,385 patients who underwent FET. After applying the inclusion and exclusion criteria, 254 patients diagnosed with CE were eligible for inclusion. Of these, 119 patients received antibiotics alone, whereas 135 were treated with a combination of doxycycline and vaginal Lactobacillus. All patients underwent embryo transfer within 6 months following treatment. The general characteristics and pregnancy outcomes of the first FET cycle post-treatment were compared between the two groups. Results: There were no statistically significant differences between the two groups in terms of general characteristics, clinical pregnancy rate, early miscarriage rate, and ectopic pregnancy rate. Patients who received a combination of doxycycline and Lactobacillus showed a higher biochemical pregnancy rate compared to those who received doxycycline alone, though this difference was not statistically significant (70.37% vs. 64.71%, P=0.313). Furthermore, the incidence rate of premature rupture of membranes was lower in the doxycycline-Lactobacillus group than in the doxycycline group (50.00% vs 33.33%, P=0.037). Conclusions: Although this study observed the potential benefits of the antibiotic and vaginal probiotic treatment regimen in increasing the biochemical pregnancy rate and reducing the incidence of premature rupture of membranes, the current findings are insufficient to recommend the combined use of antibiotics and vaginal Lactobacillus as an intervention to improve reproductive outcomes in infertile patients with CE.