Randomized Clinical Trial: The Impact of Vaginal Synbiotic Supplementation on the Assisted Reproductive Technology (Art) Outcomes and Lactobacillus Status of Genital Tract in Infertile Women Prior to Frozen Embryo Transfer Publisher



Jafari S ; Jabarpour M ; Aleyasin A ; Talebian M ; Shabani Nashtaei M ; Hosseini Mousa S
Source: Middle East Fertility Society Journal Published:2026

Abstract

Objective: The aim of this study was to investigate the efficacy of Lactovage suppository on genital tract bacterial culture and assisted reproductive technology (ART) outcomes in infertile women undergoing frozen embryo transfer (FET). Methods: A randomized, double-blind, placebo-controlled trial was conducted on 156 women scheduled for FET. Participants were randomly divided into two equal groups, with one group receiving a daily intravaginal capsule containing Lactobacillus and maltodextrin (intervention group) for 30 days, while the other received a placebo capsule with an inactive ingredient (control group) over the same period. After the intervention, data related to Lactobacillus status (vaginal and uterine) and ART outcomes were analyzed. Results: Baseline characteristics were comparable between groups. The intervention group showed significantly higher chemical (45.5% vs. 28.9%, P = 0.034) and clinical pregnancy rates (42.9% vs. 27.6%, P = 0.048), while ongoing pregnancy and implantation rates were higher but not statistically significant. Miscarriage rates were similar between groups, and multiple pregnancy occurred only in the control group. Although vaginal and uterine Lactobacillus positivity was more frequent in the synbiotic group, this difference was not significant; however, Lactobacillus-positive vaginal and uterine status was associated with higher pregnancy rates, particularly in the intervention group. Conclusion: Intravaginal synbiotic supplementation before FET may be associated with improved chemical and clinical pregnancy rates in women undergoing ART. While other outcomes did not differ significantly between groups, a Lactobacillus-positive genital tract environment was linked to more favorable pregnancy outcomes, particularly in the synbiotic group. Larger multicenter studies are needed to confirm these findings. Trial registration: This study was retrospectively registered in the Iranian website (www.irct.ir) for clinical trials registration (http://www.irct.ir: IRCTID: IRCT20110602006689N5). © The Author(s) 2026.