To evaluate the association between the duration of cryopreservation and reproductive and neonatal outcomes using a meta-analysis.
Approach:
Study Inclusion: A total of 17 studies were included, comparing outcomes between frozen-thawed embryo transfer (FET) ≤12 vs >12 months post-storage.
Meta-Analysis: The meta-analysis was conducted using Review Manager 5.3 software.
Key Findings:
Shorter storage (≤12 months) was associated with higher odds of live birth rate (OR 1.19, 95% CI 1.09-1.30), biochemical pregnancy rate (OR 1.44, 95% CI 1.19-1.75), and clinical pregnancy rate (OR 1.24, 95% CI 1.12-1.37).
The multiple pregnancy rate was higher with shorter storage (OR 1.26, 95% CI 1.03-1.55), but this was likely influenced by uncontrolled confounding.
Maternal age was identified as a significant effect modifier for live birth and clinical pregnancy rates.
No significant differences were found in survival rate, miscarriage rate, implantation rate, ectopic pregnancy rate, preterm birth, low birth weight, congenital malformations, or sex ratio.
Interpretation:
Shorter storage duration was associated with improved pregnancy rates; however, high heterogeneity and reliance on specific cohorts limit the generalizability of these findings. Causal inference is not possible due to the retrospective nature of the studies.
Limitations:
All studies were retrospective cohorts, limiting causal inference.
High heterogeneity and wide prediction intervals may affect the reliability of the results.
Inconsistent confounding adjustment across studies.
Dependence on studies from specific regions affects generalizability.
Dichotomous classification does not capture potential dose-response relationships.
Conclusion:
Storage duration should not be used alone to prioritize transfer timing; clinical decisions must consider patient readiness, embryo quality, and clinic-specific protocols.
