Impact of intrauterine infusion of human umbilical cord blood mononuclear cells on reproductive outcomes in patients with thin endometrium undergoing frozen embryo transfer

Objective This study aims to assess the effects of intrauterine infusion of human umbilical cord blood mononuclear cells (HUCBMCs) on reproductive outcomes in patients with thin endometrium undergoing frozen embryo transfer (FET). Design Prospective cohort study. Study Participants This study enrolled 134 patients diagnosed with thin endometrium who underwent FET procedures between January 2022 and December 2023. The cohort was stratified into two groups: a treatment group receiving HUCBMCs infusion (n = 35) and a control group (n = 99). Methods Participants were allocated into two groups: the HUCBMCs group and the control group, based on the administration of HUCBMCs intrauterine infusion. Reproductive outcomes were monitored for all participants. The primary outcome measure was live birth, while secondary outcomes encompassed endometrial characteristics (thickness, pattern, and endometrial–subendometrial (ES) blood flow distribution pattern), implantation rate, biochemical pregnancy, clinical pregnancy, ongoing pregnancy, miscarriage rate, and obstetric outcomes. Multivariable logistic regression analyses were employed to ascertain the independent effects of HUCBMCs. Results No significant improvement in endometrial characteristics was noted following the infusion of HUCBMCs. Similarly, the live birth rate did not differ significantly between the groups, with the HUCBMCs group exhibiting a live birth rate of 27.6% (8 out of 29 patients), comparable to the control group 27.1% (19 out of 70 patients) ( P = 0.964). Additionally, when compared to the control group, the HUCBMCs group showed no statistically significant differences in implantation rate, biochemical pregnancy, clinical pregnancy, and ongoing pregnancy, as determined by multivariate logistic regression analysis (OR 0.46, 95% CI 0.16–1.32; OR 0.74, 95% CI 0.24–2.26; OR 0.79, 95% CI 0.26–2.41; OR 0.96, 95% CI 0.13–7.22, respectively). Notably, the miscarriage rates were 38.5% in the HUCBMCs group and 36.7% in the control group. Moreover, blastocyst transfer was associated with a significantly higher likelihood of live birth compared to cleavage embryo transfer, as evidenced by both crude and multivariate logistic regression analyses (OR 6.52, 95% CI 2.22–19.20; OR 7.86, 95% CI 2.20–28.08). No adverse effects were observed in the HUCBMCs group. Conclusion Our findings indicate that although HUCBMCs infusion was deemed safe, there was no statistically significant improvement in reproductive outcomes between the HUCBMCs group and the control group. The miscarriage rate remained high among patients with thin endometrium. However, blastocyst transfer may be associated with a higher live birth rate compared to cleavage embryo transfer.