P-232 Beyond 12 months, blastocyst cryostorage duration in close system affects live birth rate: a monocentric retrospective study

Abstract

Abstract Study question In order to evaluate the effect of blastocyst cryopreservation duration on live birth rate (LBR). Summary answer Blastocyst cryopreservation duration negatively affects live birth rate when blastocysts are vitrified in complete close system for more than 12 months. What is known already With the development of embryo vitrification, frozen-thawed program embryo transfer has been widely used in the past decade. However, the association between cryopreservation duration and frozen blastocyst transfer outcomes are limited. So far, very few studies have provided evidence on the relationship between blastocyst storage duration and LBR. Study design, size, duration This monocentric retrospective study included 1267 women (n = 1462 cycles) who underwent single frozen blastocyst transfer. Duration of vitrification in close system was categorized into five groups included 2144 frozen blastocysts (Day 5/6) : <3 months (n = 417; mean female age = 32.6 ± 4.74y), 3-6 months (n = 596; mean female age = 33.2 ± 4.96y), 6-12 months (n = 440; mean female age = 33.4 ± 4.83y), 12-36 months (n = 512; mean female age = 32.6 ± 4.75y), and >36 months (n = 179; mean female age = 31.1 ± 3.90y). Participants/materials, setting, methods Clinical pregnancy and live birth outcomes were compared between the cohorts stratified according to blastocyst cryostorage duration. A binary multivariate logistic regression was performed, adjusting for confounders: female age at vitrification, male age, ART technique (IVF or ICSI) and endometrial preparation protocol (spontaneous, substituted and stimulated FET cycle). Multivariable analysis was used to assess the association between crystorage duration of vitrified blastocyst and LBR. All frozen blastocyst transfers were realized in spontaneous, substituted or stimulated cycles. Main results and the role of chance After multivariable analysis, live birth rate was significantly different depending on blastocyst cryostorage duration (all groups combined) (p = 0.033): live birth rate was significantly lower when blastocyst cryostorage duration was between 12-36 months (OR 0.740 IC95%[0.558; 0.981] p = 0.036) and beyond 36 months (OR 0.674 IC95%[0.456; 0.986] p = 0.044) compared to less than 3 months of blastocyst cryostorage duration. However, no significant impact of blastocyst cryostorage duration was observed on clinical pregnancy rate (p = 0.52). Limitations, reasons for caution Our study was limited by its retrospective design with restricted samples. Wider implications of the findings This study provides new findings on the effect of blastocyst cryostorage duration with a significant impact on LBR beyond 12 months of vitrification in close system. However, it’s crucial to confirm that cryostorage duration doesn’t lead to adverse obstetric and perinatal outcomes after vitrified blastocyst transfer. Trial registration number not applicable