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Purpose <p>To investigate how embryo vitrification duration affects frozen-thawed transfer outcomes, focusing on the interaction between age (at transfer and at freezing) and storage time.</p> Methods <p>This retrospective cohort study included 13,054 first vitrified embryo transfers (2015–2025). Cycles were divided by cryopreservation duration: ≤ 0.5, 0.5–2, 2–5, and &gt; 5&#xa0;years. Primary outcomes were clinical pregnancy, implantation, and live birth rates; secondary outcomes included biochemical pregnancy, miscarriage, ectopic pregnancy, and multiple pregnancy rates. Multivariate logistic regression adjusted for confounders, followed by age-stratified analyses and interaction tests. Subgroup analyses used age at transfer (ROC cutoff 36&#xa0;years) and at freezing (cutoff 34.5&#xa0;years).</p> Results <p>Compared to ≤ 0.5&#xa0;years, the &gt; 5&#xa0;years group showed lower clinical pregnancy (aOR = 0.757, <i>P</i> = 0.036), implantation (aOR = 0.604, <i>P</i> = 0.001), and live birth rates (aOR = 0.881, <i>P</i> = 0.003). For 2–5&#xa0;years, only the live birth rate decreased (aOR = 0.875, <i>P</i> = 0.049). Age significantly interacted with freezing duration (<i>P</i> = 0.001). Women aged ≤ 34.5&#xa0;years at freezing also exhibited a dose–response decline in live birth rates with longer storage.</p> Conclusions <p>Long-term cryopreservation (&gt; 5&#xa0;years) has an adverse effect on the outcomes of frozen-thawed embryo transfer, but this effect is observed only in younger women (≤ 35&#xa0;years). In older women (≥ 36&#xa0;years), the deterioration of the uterine environment may mask the additional risks associated with prolonged cryopreservation. Clinicians should make individualized decisions regarding the use of long-term cryopreserved embryos by considering both the patient’s age at the time of transfer and the age of the embryos at the time of cryopreservation.</p>

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The effect of embryo vitrification duration on frozen-thawed transfer outcomes: the key moderating role of age—a retrospective cohort study of 13,054 cycles

  • 期刊论文

  • 发表日期：

    2026年7月27日

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  • Yongxuan Ji,
  • Ying Zhang,
  • Huanze Cao,
  • Ning Zhang

摘要

Purpose

To investigate how embryo vitrification duration affects frozen-thawed transfer outcomes, focusing on the interaction between age (at transfer and at freezing) and storage time.

Methods

This retrospective cohort study included 13,054 first vitrified embryo transfers (2015–2025). Cycles were divided by cryopreservation duration: ≤ 0.5, 0.5–2, 2–5, and > 5 years. Primary outcomes were clinical pregnancy, implantation, and live birth rates; secondary outcomes included biochemical pregnancy, miscarriage, ectopic pregnancy, and multiple pregnancy rates. Multivariate logistic regression adjusted for confounders, followed by age-stratified analyses and interaction tests. Subgroup analyses used age at transfer (ROC cutoff 36 years) and at freezing (cutoff 34.5 years).

Results

Compared to ≤ 0.5 years, the > 5 years group showed lower clinical pregnancy (aOR = 0.757, P = 0.036), implantation (aOR = 0.604, P = 0.001), and live birth rates (aOR = 0.881, P = 0.003). For 2–5 years, only the live birth rate decreased (aOR = 0.875, P = 0.049). Age significantly interacted with freezing duration (P = 0.001). Women aged ≤ 34.5 years at freezing also exhibited a dose–response decline in live birth rates with longer storage.

Conclusions

Long-term cryopreservation (> 5 years) has an adverse effect on the outcomes of frozen-thawed embryo transfer, but this effect is observed only in younger women (≤ 35 years). In older women (≥ 36 years), the deterioration of the uterine environment may mask the additional risks associated with prolonged cryopreservation. Clinicians should make individualized decisions regarding the use of long-term cryopreserved embryos by considering both the patient’s age at the time of transfer and the age of the embryos at the time of cryopreservation.