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Fertility After 35 May Not Just Be About Eggs, Scientists Say
0 Share Newsweek is a Trust Project member See more of our trusted coverage when you search. Prefer Newsweek on Google to see more of our trusted coverage when you search. Fertility after 35 is often discussed in terms of egg quality and ovarian reserve.
But new research suggests the uterus itself may also play an important role.
A study published in Cell Host & Microbe found that age-related changes in the uterine microbiome, the community of bacteria living in the womb, may affect how receptive the uterus is to an embryo.
The findings suggest fertility decline after 35 may not be explained by the ovaries alone.
“Reproductive aging has traditionally been attributed mainly to a diminished ovarian reserve and reduced embryo quality,” said corresponding author Rong Li, a physician at Peking University Third Hospital in Beijing, China. “However, successful pregnancy also depends on a healthy and receptive endometrium.”
The endometrium is the inner lining of the uterus, where an embryo must implant for pregnancy to begin.
In the study, researchers analyzed endometrial samples from 149 women aged 20 to 45 who were being treated for infertility.
The participants were divided into three age groups: under 30, 30 to 35 and over 35.
The researchers found that younger women had a greater abundance of Lactobacillus bacteria in the endometrium than women in the two older groups.
One strain in particular, Lactobacillus gasseri, declined with age.
“One finding that surprised us was that overall microbial diversity did not change markedly across the different age groups,” Li says. “Instead, the major differences involved particular bacterial species.”
When researchers followed some participants for a year, 93 underwent embryo transfer and 56 achieved clinical pregnancy.
Pregnancy rates did not differ significantly between the age groups, but women who became pregnant had higher endometrial levels of Lactobacillus than those who did not.
The team then investigated how L. gasseri might influence the uterine lining. Laboratory tests suggested the strain had antioxidant and anti-inflammatory properties and adhered strongly to endometrial cells.
Researchers also examined a component produced by the bacterium, known as exopolysaccharides, or EPS, which appeared to help protect human endometrial stromal cells from signs of aging .
In experiments involving older mice, treatment with EPS derived from L. gasseri was linked to higher embryo implantation rates.
Another report on the study noted that aged mice given daily intravaginal L. gasseri showed less endometrial senescence and higher implantation rates.
The findings are preliminary and do not mean women trying to conceive should start using bacterial supplements.
For people trying to conceive after 35 , researchers say the conversation may need to move beyond eggs alone and include whether the endometrium is ready to support implantation.
Newsweek reached out to Cell Press for comment via email.
Li, M., Li, S., Zheng, D., Liao, B., Niu, H., Wang, Y., Liu, X., Pan, H., Yu, Y., Zhou, P. and Li, R. (2026). Lactobacillus gasseri postbiotics ameliorate age-related decline in endometrial receptivity. Cell Host & Microbe . [online] doi:10.1016/j.chom.2026.06.018.
Contact Newsweek editors on this story: Kara Dolman and Gray R. Thomas
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