Uterine Bacteria Lactobacillus gasseri Linked to Fertility in Women Over 35, Study Finds

A study published in Cell Host & Microbe reveals that the uterine bacterium Lactobacillus gasseri declines with age, potentially impacting endometrial receptivity in women over 35. Led by Dr. Rong Li of Peking University Third Hospital, researchers found that while overall microbial diversity remains stable, pregnant women host higher levels of Lactobacillus. In laboratory tests, postbiotic exopolysaccharides from L. gasseri protected human cells against aging and boosted embryo implantation in older mice. However, researchers caution that human trials are still needed and warn against self-medicating with unvalidated commercial supplements.

Lactobacillus gasseri age decline

• ▪The study found that overall endometrial microbial diversity did not change significantly across different age groups, with differences instead limited to specific bacterial species.
• ▪A study published in Cell Host & Microbe on August 6, 2026, shows that the abundance of the bacterium Lactobacillus gasseri in the endometrium declines as women age.
• ▪Researchers led by Rong Li analyzed endometrial samples from 149 women aged 20 to 45 undergoing infertility treatment, finding that the youngest group had significantly higher Lactobacillus abundance than older groups.

Endometrial microbiome pregnancy rates

• ▪The clinical pregnancy rates among the 93 study participants did not differ significantly across the three age groups analyzed in the study.
• ▪Among five Lactobacillus strains analyzed, Lactobacillus gasseri demonstrated the strongest adhesion to endometrial cells and the highest antioxidant and anti-inflammatory properties.
• ▪A one-year follow-up of 93 study participants who underwent embryo transfers showed that women who achieved clinical pregnancy had a higher endometrial abundance of Lactobacillus than those who did not.

Bacterial exopolysaccharides embryo implantation

• ▪Older mice treated with exopolysaccharides derived from Lactobacillus gasseri showed higher embryo implantation rates than untreated older mice.
• ▪Exopolysaccharides derived from Lactobacillus gasseri protected human endometrial stromal cells against cellular changes associated with aging.

Postbiotic fertility treatment potential

• ▪Corresponding author Rong Li cautioned women against self-medicating with over-the-counter Lactobacillus gasseri products, noting they have not been validated to treat infertility.
• ▪The researchers noted that the study is early-stage and observational in humans, meaning it cannot prove that uterine microbiome changes cause endometrial aging or poor pregnancy outcomes.