Probiotics for reproductive health

Positive signal: A 2023 RCT (n=316) found vaginal probiotics before frozen embryo transfer reduced miscarriage from 19.1% to 9.5%. In blastocyst transfers, live birth rate was 35.7% vs. 22.2%.

Important caveat: A separate double-blind RCT found 10 days of vaginal Lactobacillus supplementation was insufficient to correct unfavorable vaginal microbiota. Duration matters — short courses may not be enough.

A non-Lactobacillus-dominant vaginal microbiome has been associated with lower IVF implantation and pregnancy rates across multiple studies, suggesting this is a real and potentially modifiable factor.

The gut-reproductive axis is also active: gut microbiome diversity affects estrogen metabolism through the estrobolome. Oral probiotics may complement vaginal approaches.