Longer frozen embryo storage linked to lower live birth rates in retrospective cohort study
Photo by AKSHAY MP / Unsplash
Key Takeaway
Consider embryo storage duration in FET planning, as longer storage was associated with lower live birth rates.
This retrospective cohort study analyzed 4205 infertile patients who underwent frozen-thawed embryo transfer (FET) with cleavage-stage embryos. The intervention was post-vitrification storage duration categorized into four groups: G1 (<3 months, reference), G2 (3-6 months), G3 (6-12 months), and G4 (>12 months). The primary comparator was G1 (<3 months storage).
Main results showed live birth rates significantly decreased with longer storage duration. The adjusted odds ratios (aORs) were 0.82 for G2 (95% CI: 0.707-0.952), 0.743 for G3 (95% CI: 0.579-0.954), and 0.624 for G4 (95% CI: 0.476-0.818). Miscarriage rates significantly increased beyond 6 months storage, with aORs of 1.652 for G3 (95% CI: 1.085-2.515) and 1.674 for G4 (95% CI: 1.06-2.643). Biochemical and clinical pregnancy rates also decreased significantly beyond 12 months storage.
Safety data and adverse events were not reported in the study. Key limitations include the observational design, which cannot establish causality, and the lack of reported absolute numbers for outcomes. The study did not report primary outcome, follow-up duration, or setting details.
For clinical practice, these findings suggest an association between longer embryo storage and reduced reproductive success, but the retrospective nature requires cautious interpretation. The evidence may inform discussions about optimal timing for frozen embryo transfers, though prospective studies are needed to confirm these observations.
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View Original Abstract ↓
PurposeTo investigate the impact of storage duration after vitrification of cleavage-stage embryos on pregnancy and perinatal outcomes.MethodsA retrospective study was conducted on 4205 infertile patients underwent frozen-thawed embryo transfer (FET) between January 2020 and January 2025, categorized by post-vitrification storage duration of their embryo: G1 (12 months, n = 366). Multivariate logistic and linear regression analyses were used to determine independent effects of storage duration on pregnancy and perinatal outcomes among groups. Propensity score matching was employed to control confounders, including age, infertility duration, type, and etiology.ResultsRegarding pregnancy outcomes, live birth rate significantly decreased with storage duration (using G1 as reference; G2: adjusted odds ratio [aOR] = 0.82, 95% CI [0.707-0.952], similarly hereinafter; G3: 0.743, 0.579-0.954; G4: 0.624, 0.476-0.818). The miscarriage rate significantly increased with increasing storage duration beyond 6 months (G2: 1.268, 0.967-1.663; G3: 1.652, 1.085-2.515; G4: 1.674, 1.06-2.643). Biochemical pregnancy (G2: 0.883, 0.764-1.02; G3: 0.848, 0.669-1.075; G4: 0.705, 0.547-0.91) and clinical pregnancy rates (G2: 0.885, 0.766-1.022; G3: 0.848, 0.669-1.075; G4: 0.715, 0.554-0.922) significantly decreased with increasing storage duration beyond 12 months. Regarding perinatal outcomes, gestational age significantly decreased with increasing storage duration beyond 6 months (G1 as reference; G2: P = 0.128; G3: P = 0.023; G4: P = 0.008).ConclusionOverall, prolonged storage duration of vitrified cleavage-stage embryos negatively correlates with pregnancy and perinatal outcomes, particularly after 6 or 12 months.
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