Combined oral antibiotics and intrauterine perfusion can improve in vitro fertilization and embryo transfer pregnancy outcomes in patients with chronic endometritis and repeated embryo implantation failure

Repeated implantation failure (RIF) is defined as the inability to conceive following 3 or more consecutive embryo transfer cycles and each cycle transfer 1 ~ 2 high-quality embryos [1‐3] and affects 12%–46% of patients experiencing infertility [3], which have caused great psychological distress to women [4]. RIF can result from a variety of causes, such as anomalies in the uterine cavity, endometrial non-receptivity, immunological factors, and developmental origins [3, 5]. Over recent years, an expanding body of research has shown that less receptive endometrium caused by local immune dysregulation may be the main cause of RIF [6].

Chronic endometritis (CE), which cannot be diagnosed using ultrasound and hysterosalpingography (HSG), is a chronic inflammatory condition of the endometrium without clear clinical signs. Immunohistochemistry has revealed the presence of plasma cells in the endometrial stroma. In the endometrium, CE generates an aberrant immunological milieu that results in the generation of abnormal levels of inflammatory mediators [7]. This decreases the endometrial capacity to receive embryos, which prevents implantation.

Diagnosis of CE is complicated and difficult. Currently, there are no universal diagnostic methods for endometritis. On hysteroscopy (HSC) [8], local endometrial redness and local or diffuse endometrial congestion are seen as "strawberry signs” in addition to endometrial interstitial edema, a pale and convex surface, and multiple tiny polyps. The identification of CD138 + cells by histopathology after curettage is considered a simple and objective method [9]. Among the many methods, five plasma cells per high-power field (HPF) is the most reliable method [10]. Intrauterine microbial detection can also be used as an auxiliary method, which is more complex to operate and has many factors that affect the results. In our study, we referred to hysteroscopic and histopathological findings to diagnose CE [11].

CE treatment involves administration of various antibiotics [10], and doxycycline combined with metronidazole is considered effective [12]. Doxycycline is a broad-spectrum antibiotic that is effective against both Gram-positive and Gram-negative bacteria, while metronidazole is a broad-spectrum anti-anaerobic bacteria drug that shows good effects against most bacilli. While oral antibiotics are mainly used to treat CE, improvements in pregnancy outcomes are not evident [13‐15]. In a previous study [16] of patients with RIF, one group received doxycycline combined with metronidazole orally and the other group received a ciprofloxacin intrauterine infusion based on oral medication. After subsequent in vitro fertilization and embryo transfer (IVF-ET), there were no differences in embryo implantation rates, clinical pregnancy rates, or live birth rates between the two groups.

Other treatments have been investigated to achieve better results. Intrauterine administration is considered an effective method for the treatment of intrauterine diseases because of its rapid onset of action and high local drug concentrations. Antibiotic therapy in combination with platelet-rich plasma(PRP) is said to improve pregnancy outcomes in these patients, but the procedure has some limitations because it is a blood product and carries the risk of infection [17]. A recent study showed that intrauterine antibiotic infusions led to successful pregnancies in three patients with CE, for whom IVF had previously failed [15]. Oral doxycycline combined with the local administration of antibiotics can significantly improve implantation and pregnancy rates, and the effect is better than that of oral antibiotics alone [16, 18]. Another study showed that intrauterine administration of dexamethasone successfully improved endometrial receptivity. Gentamicin, the main drug used in the treatment of endometritis, is cheap and effective and has been widely used in obstetrics and gynecology [19]. Therefore, doxycycline combined with antibiotics and dexamethasone for the treatment of CE is feasible and worthy of further investigation.

In this study, we used doxycycline combined with intrauterine perfusion (gentamicin and dexamethasone) to further investigate whether this combination improves pregnancy outcomes, compared with oral administration of antibiotics alone, to find a new alternative method for the treatment of CE and to provide a new perspective for the treatment of RIF.

RIF, which directly affects the pregnancy rate, is a difficult problem for reproductive doctors. In recent years, researchers have made significant efforts to study the pathogenesis and treatment of RIF with little success. Recent studies suggest that endometrial immune disorders may lead to immune cell abnormalities, involving natural killer (NK) cells, macrophages, regulatory T cells (Tregs), and other functional abnormalities, leading to maternal–fetal immune disorders and embryo implantation disorders [22]. The use of immunosuppressants, including intravenous immunoglobulin [23], intrauterine infusion of peripheral blood mononuclear cells [24], tacrolimus [25], subcutaneous administration of granulocyte colony-stimulating factor [26], and prednisone [27], have also been shown to improvement RIF and enhance the receptivity of the endometrium and improve the success rate of pregnancy. Scientists are even combining knowledge with computer science through machine learning algorithms, using artificial intelligence (AI) tools to analyze information about RIF patients and embryos to predict pregnancy outcomes [28]. In the near future, it may even be possible to use Artificial Womb Technology (AWT) to solve pregnancy problems in such patients [29].

Endometritis is an unsolved problem today. It is a significant contributor to repeated implant failures and other fertility problems. The clinical symptoms of endometritis are often mild and easily ignored. Endometritis is a complicated disease. First of all, the diagnostic methods and diagnostic criteria of endometritis are not uniform. Secondly, the treatment of endometritis is mainly empirical, the therapeutic effect is not ideal and easy to produce drug resistance. Finally, it is difficult to have a non-invasive way to check the effect of treatment after treatment.

Dexamethasone, a glucocorticoid, has powerful immunomodulatory effects. Zhang [18] administered an intrauterine infusion of dexamethasone to eight patients with RIF and found that the proportion of NK cells was downregulated in samples taken by endometrial biopsy. Seven patients successfully became pregnant after cryopreserved ET. Three patients delivered healthy babies at term without any pregnancy complications, suggesting that prednisone can downregulate the proportion of NK cells, improve endometrial receptivity, and promote embryo implantation. Huang [30] treated patients with RIF using prednisone and found that the proportion of Tregs and IL-10, which are indicators of immune tolerance, was significantly increased, whereas IL-17A, IL-23, and other proinflammatory factors were significantly decreased. After treatment, five patients with RIF successfully became pregnant and four had live births (n = 19). It has been suggested that prednisone can improve local immunity and place the endometrium in a sensitive phase, which is beneficial for embryo implantation.

In a study of patients with RIF, Kotaro [31] found that 33.7% of women with RIF infertility were diagnosed with CE. In a 10-year study of patients with RIF, Kotaro [32] also found that 31.4% of the women concurrently had CE and 7.8% of women with RIF had multi-drug-resistant CE, with a steady increase in multi-drug resistance (odds ratio [OR], 8.27; 95% confidence interval [CI], 2.58–26.43; P < 0.001). Therefore, a more effective method may be required to treat CE. Intrauterine perfusion can enable the drug to directly act more locally, quickly, and with a high concentration to reduce systemic adverse reactions. Intrauterine perfusion is a commonly used treatment in obstetrics and gynecology, and it is the first-line treatment for endometritis during labor [32], with high levels of safety and effectiveness. In animal experiments, intrauterine infusion of gentamicin and dexamethasone in buffaloes with endometritis was shown to significantly increase the number of pregnancies [32]. Zhang [18] treated patients with RIF/CE using an intrauterine infusion of dexamethasone combined with gentamicin/clindamycin, with a 60% cure rate of CE, indicating that gentamicin has good therapeutic effect on CE. The clinical pregnancy and live birth rates of patients with treated RIF/CE were increased after cryo-ET, not only because of the therapeutic effect of gentamicin on CE but also because dexamethasone treatment can increase endometrial embryo acceptance and improve pregnancy outcomes. Therefore, we believe that oral doxycycline and metronidazole combined with an intrauterine infusion of gentamicin and dexamethasone may achieve an improved therapeutic effect.

Our inclusion requirements are quite tight, which is why we only have a tiny number of examples. Another important factor was that we did not include these patients who did not have their CD138 levels checked again or who did not have two standardized hysteroscopies. Because the patients we included were retransplanted after RIF, and some of the patients had no optimal embryo, we had no way to evaluate the effectiveness of the method. Further decreasing the number of instances we considered was the fact that some patients were also not included in other therapies.

To assess the effect of antibiotic treatment on CE and the integrity of the study, we initially planned to include women with RIF/CE and either placebo or no treatment in the control group. However, we would not find patients in the hospital who were diagnosed with RIF/CE and did not receive any treatment, it's not ethical. We also excluded patients who were treated with other regiments. Given the large number of reports on the efficacy of oral antibiotics (doxycycline and metronidazole) in the treatment of CE, we compared whether oral antibiotics combined with an intrauterine infusion of antibiotics were more effective than oral antibiotics alone.

In conclusion, our results show that the use of oral antibiotics (doxycycline and metronidazole) combined with intrauterine perfusion (gentamicin and dexamethasone) are beneficial for patients with RIF/CE. When D3 cleavage were transplanted, the combination group showed higher implantation, clinical pregnancy, and live birth rates. These drugs are widely used in the fields of obstetrics and gynecology and have no teratogenic effect. We plan to conduct further animal experiments to elucidate the specific molecular mechanisms.