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Probiotic Supplementation Increases Endometrial Thickness in PCOS Women Undergoing IUI
An 8-week probiotic intervention in women with polycystic ovary syndrome (PCOS) undergoing intrauterine insemination (IUI) produced a statistically significant increase in endometrial thickness compared to placebo (β = 0.618, 95% CI: 0.167–1.069, p = 0.008), though differences in clinical and chemical pregnancy rates did not reach statistical significance in this small trial.
What Was Studied
This trial investigated whether oral probiotic supplementation could improve fertility-related outcomes — including pregnancy rates, endometrial thickness, and follicular development — in women with PCOS preparing to undergo IUI. The rationale draws on emerging evidence that gut and reproductive tract microbial dysbiosis may negatively influence implantation and conception, making probiotics a plausible adjunct to assisted reproduction protocols.
How It Was Studied
This was a randomized, double-blind, placebo-controlled trial enrolling 100 women aged 19 to 37 years, all diagnosed with PCOS and scheduled for IUI. Participants were allocated equally (1:1) to either a probiotic supplement or an identical placebo, taken for 8 weeks following ovulation induction. Primary outcomes assessed after IUI included chemical pregnancy rate, clinical pregnancy rate, number of dominant follicles, and endometrial thickness. Groups were well-matched at baseline, with no significant differences in demographic or paraclinical characteristics.
What Was Observed
- Endometrial thickness was meaningfully greater in the probiotic group, and regression analysis confirmed that probiotic supplementation was the only significant predictor of this increase (β = 0.618, 95% CI: 0.167–1.069, p = 0.008). This suggests a specific effect on uterine lining development rather than a general hormonal or ovarian influence.
- Clinical pregnancy rate was numerically higher in the probiotic group but did not reach statistical significance — 14% of probiotic recipients achieved a clinical pregnancy compared with 4% in the placebo group (p = 0.081). While the absolute difference of 10 percentage points is clinically notable, the study was likely underpowered to confirm this difference reliably.
- Chemical pregnancy rate showed a similar directional trend without statistical significance: 16% in the probiotic group versus 12% in the placebo group (p = 0.564), indicating insufficient evidence to attribute this difference to the intervention.
- Dominant follicle counts did not differ between groups (p > 0.05), suggesting probiotics did not influence ovarian follicular response in this cohort, and any benefit appears to act through endometrial rather than ovarian mechanisms.
Why This Matters
Endometrial receptivity is a recognized barrier to successful implantation in PCOS, and few low-risk interventions have shown measurable effects on uterine lining thickness in this population. The finding that a standardized probiotic regimen significantly improved endometrial thickness adds to a growing body of research linking the microbiome to reproductive tract physiology. If replicated in larger studies, this mechanism could have implications for how adjunct therapies are designed for women undergoing assisted reproduction.
How to Read This Result
With only 50 participants per arm and pregnancy rates as low as 4–14%, this trial was substantially underpowered to detect differences in pregnancy outcomes, and the endometrial thickness finding — while statistically significant — should be considered preliminary until confirmed in larger, adequately powered studies.
Limitations
The abstract does not explicitly report study limitations.