Genital tract dysbiosis in infertile women with a history of repeated implantation failure and pilot study for reproductive outcomes following oral enteric coating lactoferrin supplementation

Purpose We prospectively investigated if oral enteric coating lactoferrin supplementation improves the reproductive outcomes in infertile women with a history of repeated implantation failure (RIF) and non- Lactobacillus -dominant ( Lactobacillus rate < 90%) microbiota (NLDM) in vaginal secretions (VS)/endometrial fluid (EF). Methods Paired VS/EF samples were obtained from RIF women and control infertile women (non-RIF group) for microbiome analysis. Chronic endometritis (CE) was diagnosed histopathologically and hysteroscopically. In a pilot study, oral enteric coating lactoferrin (700 mg/day, at least 28 consecutive days) was administered to eligible patients with NLDM in VS/EF. Their reproductive outcomes in the subsequent vitrified-warmed embryo transfer cycles were followed up. Results While CE was more prevalent (OR 2.41, 95% CI 1.02–5.63, p = 0.042) in the RIF group (29.1%, n = 117) than in the non-RIF group (14.5%, n = 55), The NLDM rate was similar between the two groups (44.4 vs 52.7%). Lactoferrin supplementation improved NLDM in 43.2% of RIF women ( n = 37). Within the RIF group, the live birth rate in the subsequent cycles was higher (OR 10.67, 95% CI 1.03 − 110.0, p = 0.046) in women with improved microbiota (57.1%, n = 14) than in those with unimproved microbiota (11.1%, n = 9). Conclusion Unlike CE, NLDM was not unique to RIF but was common in infertile women. Although the therapeutic effect of the oral lactoferrin supplementation on NLDM was limited in a pilot study, the reproductive outcomes were better in RIF women who overcame NLDM than in those who failed. Randomized controlled trials are required to confirm the results. Trial registration number and date for prospectively registered trials UMIN-CTR 000036990, June 7, 2019.