Research in a 2026 study found that bacteria detected on the embryo transfer catheter were linked to lower live birth rates, likely reflecting the patient’s own microbiome being carried into the uterus during transfer.
Microbiome
A 2026 study showed that women with unexplained infertility who didn’t get pregnant after IVF had a more diverse endometrial microbiome with fewer Lactobacillus bacteria, and metabolites produced by other bacteria may influence how the uterine lining functions during implantation.
The Italian Society of Fertility and Sterility and Reproductive Medicine (SIFES-MR) has issued new guidelines on 28 IVF add-ons, outlining which may help in certain situations, which lack evidence, and which should be limited to research.
A 2025 study found that RIF and RPL patients with abnormal EMMA & ALICE results that had antibiotic and/or probiotic treatment showed similar pregnancy rates to those with normal EMMA & ALICE results.
Researchers in a 2023 study found that probiotic supplementation had no impact on positive hCG pregnancy rates, but may improve miscarriage rates.
This post reviews what research currently shows about the vaginal and endometrial microbiome and how it may relate to fertility and IVF outcomes. While Lactobacillus species are often considered beneficial and are commonly found in the reproductive tract, studies examining whether microbiome differences actually affect IVF success have produced mixed results.