Shorter cryopreservation duration associated with higher live birth and clinical pregnancy rates in FETShorter embryo storage may lead to better live birth rates

Frontiers in Medicine Published July 15, 2026 DOI ↗ Editorial oversight: Dr. Amelia Tan, PhD · Internal Medicine & Chronic Disease

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Key Takeaway

Note that shorter cryopreservation durations are associated with higher pregnancy rates, but results are limited by high heterogeneity.

This meta-analysis synthesized data from 17 studies to evaluate how cryopreservation duration (≤12 months versus >12 months) affects reproductive outcomes in patients undergoing frozen-thawed embryo transfer. The analysis indicates that shorter storage durations are associated with higher odds of live birth (OR 1.19; 95% CI 1.09-1.30), biochemical pregnancy (OR 1.44; 95% CI 1.19-1.75), and clinical pregnancy (OR 1.24; 95% CI 1.12-1.37). Additionally, a higher odds of multiple pregnancies was observed with shorter storage durations (OR 1.26; 95% CI 1.03-1.55).

The authors note several limitations affecting the strength of these findings. All included studies were retrospective cohorts, which precludes causal inference. High heterogeneity was observed across outcomes (I² ranging from 78% to 92%), and 95% prediction intervals crossed the null line. The results also showed a marked dependence on Chinese cohorts and inconsistent confounding adjustments. Furthermore, the association between shorter storage and improved outcomes was primarily driven by maternal age and specific regional cohorts.

Clinically, these findings suggest that while shorter cryopreservation duration is associated with better pregnancy outcomes in this meta-analysis, it should not be used as a standalone factor for prioritizing transfer timing. Clinical decisions must remain individualized. The association with multiple pregnancies likely reflects confounding by embryo number rather than storage duration itself.

For many people undergoing fertility treatments, the time an embryo spends in frozen storage is a source of anxiety. They want to know if waiting longer affects their chances of success. A review of 17 different studies looked at these outcomes specifically for patients undergoing frozen-thawed embryo transfers.

The data showed that embryos stored for 12 months or less had higher odds of biochemical, clinical, and live births compared to those stored longer. The study also noted a higher rate of multiple pregnancies in the shorter storage group. However, researchers found these results were heavily influenced by the age of the mother and specific data from Chinese clinics.

It is important to remember that because these studies looked at past records rather than controlled trials, we cannot say for certain that time alone causes these differences. There was also a lot of variation between the different studies included. Doctors suggest that storage time should not be the only factor used to decide when to move forward with a transfer; every case needs an individual plan.

What this means for you:

Embryos stored for 12 months or less showed higher pregnancy odds, but maternal age and other factors also play big roles.

Common questions

Does the length of time an embryo is frozen affect the chance of a live birth?

The data shows that embryos stored for 12 months or less had higher odds of a live birth compared to those stored longer. However, this finding was influenced by factors like maternal age and specific study locations.

What are the differences in pregnancy rates based on storage time?

Patients with embryos stored for 12 months or less showed higher odds of both biochemical pregnancies and clinical pregnancies. The study also found a higher rate of multiple pregnancies in the shorter storage group.

Is it better to use shorter storage times to decide when to transfer an embryo?

While shorter storage showed better outcomes in this data, experts say storage duration should not be used alone to decide timing. Every treatment plan must be individualized based on the specific needs of the patient.

Study Details

Study typeMeta analysis

EvidenceLevel 1

PublishedJul 2026

View Original Abstract ↓

AimThis study aims to evaluate the association between the duration of cryopreservation and reproductive and neonatal outcomes using a meta-analysis.MethodsA comprehensive search was conducted in PubMed, Embase and Medline databases up to October 1, 2025. A total of 17 studies were included in the analysis and compared reproductive/neonatal outcomes between frozen-thawed embryo transfer (FET) ≤12 vs >12 months post-storage. The meta-analysis was conducted using Review Manager 5.3 software.ResultsShorter storage (≤12 months) was associated with higher odds of live birth rate(OR 1.19, 95% CI 1.09-1.30; 15 studies, I² = 78%), biochemical pregnancy rate (OR 1.44, 95% CI 1.19-1.75; 8 studies, I² = 92%), and clinical pregnancy rate (OR 1.24, 95% CI 1.12-1.37; 15 studies, I² = 85%). However, these associations were accompanied by substantial heterogeneity (I² = 78-92%), and 95% prediction intervals crossed the null line. The multiple pregnancy rate was also higher with shorter storage (OR 1.26, 95% CI 1.03-1.55), yet this association was confined to studies permitting double-embryo transfer and likely reflects uncontrolled confounding by embryo number rather than a biological benefit. Subgroup analyses revealed that the association between shorter storage and improved outcomes was primarily driven by maternal age and studies from China. Meta-regression identified maternal age as a significant effect modifier for live birth rate (OR = 0.973, P = 0.014) and clinical pregnancy rate (OR = 0.974, P = 0.025), while no significant interactions were found for biochemical pregnancy rate. There were no significant differences between the two groups in survival rate, miscarriage rate, implantation rate, ectopic pregnancy rate, preterm birth, low birth weight, congenital malformations, or sex ratio. No significant publication bias was detected by Egger’s or Begg’s tests.ConclusionAlthough shorter storage was associated with improved pregnancy rates, all studies were retrospective cohorts, precluding causal inference. High heterogeneity, wide prediction intervals, inconsistent confounding adjustment, and marked dependence on Chinese cohorts limit generalizability. The dichotomous classification cannot capture dose-response relationships, and long-term offspring outcomes remain unreported. Storage duration should not be used alone to prioritize transfer timing. Clinical decisions must remain individualized, accounting for patient readiness, embryo quality, and clinic-specific protocols.

Shorter cryopreservation duration associated with higher live birth and clinical pregnancy rates in FETShorter embryo storage may lead to better live birth rates

Common questions

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Shorter cryopreservation duration associated with higher live birth and clinical pregnancy rates in FETShorter embryo storage may lead to better live birth rates

Common questions

Study Details

Thiazolidinediones show lower hepatocellular carcinoma risk than DPP-4 inhibitors, GLP-1RAs, insulin, and sulfonylureas in this network meta-analysis

New analysis links diabetes drugs to liver outcomes in millions of patients

Clinical research that matters. Delivered to your inbox.

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