The role of the endometrial microbiome on fertility in patients with chronic endometritis

Chronic endometritis (CE), an infectious disease of the female reproductive tract, is frequently associated with reproductive failure. However, it is worth noting that not all CE patients would experience reproductive failure. This prospective study sought to identify the microbes that are associated with CE while would simultaneously affect fertility and compare with the microbes that are associated with CE but would not affect fertility. We recruited women aged between 18 and 45 years from two tertiary centers in China between October 2021 and May 2023. Demographic data, clinical data, and endometrial tissue were collected. Endometrial microbiome was detected by 16S rRNA gene amplicon sequencing and CE was diagnosed by immunohistochemistry staining with syndecan-1. A total of 100 women who achieved successful implantation through spontaneous conception and 61 women who were infertile were enrolled into this study. Of them, 19 women with normal pregnancy and 26 women with infertility had CE. CE patients with infertility had significantly different microbial diversity and compositions compared to CE patients with pregnancy. The predominant differential microbes, namely Ligilactobacillus (4.69%), Methyloversatilis (2.59%), and Stenotrophomonas (2.66%), which exhibited a high abundance, were significantly associated with infertility in CE patients. The primary differential microbes, Sphingomonas (20.48%), Faecalibacterium (6.46%), Blautia (1.62%), Escherichia_Shigella (3.27%), and Corynebacterium (1.35%) exhibited a high abundance, were associated with pregnancy in CE patients. In conclusion, the endometrial microbial composition and abundance of CE patients with infertility were significantly different from that of CE patients with successful implantation. These findings could advance our understanding of the role of endometrial microbiome on fertility in CE patients and could facilitate in the development of targeted treatment for CE.