Impact of post-vitrification storage duration on clinical outcomes of frozen-thawed cleavage-stage embryos transfer: a propensity score-matched retrospective cohort study

Purpose To investigate the impact of storage duration after vitrification of cleavage-stage embryos on pregnancy and perinatal outcomes. Methods A 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 (<3 months, n = 2,208), G2 (3–6 months, n = 1,232), G3 (6–12 months, n = 399), and G4 (>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. Results Regarding 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). Conclusion Overall, prolonged storage duration of vitrified cleavage-stage embryos negatively correlates with pregnancy and perinatal outcomes, particularly after 6 or 12 months.