Lactobacillus-dominated uterus significantly boosts pregnancy outcomes

For decades, the uterus was believed to be a sterile environment, but recent research has upended this idea, revealing a diverse microbiome that may influence fertility and reproductive health. A new review published in Reproductive and Developmental Medicine explores how microbial communities in the female reproductive tract—especially Lactobacillus spp.—affect embryo implantation, pregnancy success, and gynecological diseases.

Researchers from the University of Hong Kong analyzed recent studies on the reproductive microbiome and its effects on fertility. They found that a Lactobacillus-dominated (LD) uterine environment significantly improves pregnancy outcomes. Similarly, pregnancy success rates were higher in LD environments.

Lactobacilli help by maintaining a low pH in the reproductive tract, preventing harmful bacteria (like E. coli) from taking over. Other microbes, such as Bifidobacterium spp. (acetate producer), Prevotella spp. (acetate producer), Eubacterium spp. (Butyrate producer) and Enterobacter spp.  (propionate producer), may play a role, producing short-chain fatty acids (SCFAs) that regulate immune responses crucial for embryo implantation.

Hostile environment

The study highlights that women undergoing IVF who had a non-LD uterine microbiome were far less likely to achieve pregnancy. Additionally, disruptions in microbiota composition have been linked to conditions such as chronic endometritis, endometriosis, and recurrent implantation failure (RIF).

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“A disturbed microbiome may create a hostile environment for embryo implantation,” said Dr. Kai-Fai Lee, the corresponding author. “This could explain why some women struggle with unexplained infertility despite having no obvious reproductive issues.”

These findings underscore the need for more targeted fertility treatments, including microbiome-based interventions. The researchers suggest that probiotics or personalized treatments to restore a healthy microbiome could improve fertility outcomes, particularly for women struggling with IVF failure.