How embryo retention affects assisted reproductive technology outcomes: a systematic review and meta-analysis.

Background: Retransferring retained embryos during the embryo transfer (ET) procedure has raised concerns about its adverse effects on assisted reproductive technology (ART) outcomes. Technical challenges associated with embryo retention (ER) may compromise implantation success and lead to increased complications.

Objective: This systematic review and meta-analysis aimed to evaluate the impact of retransferring retained embryos on key ART outcomes, including clinical pregnancy rate (CPR), biochemical pregnancy rate (BPR), ectopic pregnancy rate (EP), miscarriage rate (MR), and live birth rate (LBR).

Methods: We conducted a systematic search in PubMed, Scopus, and Cochrane databases from inception to April 11, 2025. ART outcomes were extracted and pooled Mantel-Haenszel odds ratios (OR) with 95% confidence intervals (CI) were calculated under both fixed- and random-effects models. Subgroup analyses were performed based on study design (matched versus non-matched retrospective cohorts) and ET technique (afterload versus direct). Sensitivity analyses were conducted by excluding studies with high or very high risk of bias, as determined by the ROBINS-E tool.

Results: The overall analysis demonstrated that retransferring retained embryos was associated with a significant reduction in CPR (OR ≈ 0.75, 95% CI: 0.64-0.89, p < 0.001) and LBR, while substantially increasing the risk of EP (OR ≈ 2.36, p = 0.036). Subgroup analysis showed that studies with matched designs and those using the afterload ET technique exhibited more pronounced negative outcomes. Sensitivity analyses confirmed the robustness of the primary findings.

Conclusion: ER negatively impacts ART success, lowering clinical pregnancy and live birth rates and elevating the risk of ectopic pregnancy. These findings highlight the critical need to refine ET protocols and further investigate the biological mechanisms underlying ER. Future well-designed, prospective studies with standardized methodologies are warranted to optimize ER management and improve clinical outcomes.