Associations of post-thaw cleavage progression with live birth and neonatal outcomes following vitrified single cleavage-stage embryo transfer: a retrospective cohort study

Abstract

In assisted reproductive technology, extended embryo culture to the blastocyst stage with cryopreservation is currently routine, while cleavage-stage embryo transfer is still preferred when there are limited embryos or suboptimal quality. However, the effect of post-thaw cleavage progression on clinical and neonatal outcomes following single vitrified cleavage-stage embryo transfer remains underexplored. This study aimed to evaluate its associations with live birth and neonatal outcomes. This retrospective cohort study, conducted at a tertiary-care center in Northwest China, included cycles with autologous single vitrified-thawed Day 3 embryo transfers between January 2018 and December 2023. Cycles were categorized by post-thaw cleavage progression: the compacting/blastocyst group (Group 1), the group with ≥ 1 additional blastomere (Group 2), and the no-cleavage group (Group 3, reference). Associations between post-thaw cleavage progression and pregnancy/neonatal outcomes were assessed using generalized estimating equation models. A total of 4,011 cycles from 3,537 patients were categorized into three groups: Group 1 ( n = 1,138, 28.4%), Group 2 ( n = 2,485, 61.9%), and Group 3 ( n = 388, 9.7%). Group 1 and Group 2 showed significantly higher live birth rates per transfer compared with Group 3 (aRR: 2.62, 95% CI: 2.02, 3.40 and aRR: 1.79, 95% CI: 1.39, 2.31, respectively). Each one‑stage increment in cleavage progression was associated with a 52% increase in live birth probability per transfer (aRR: 1.52, 95% CI: 1.40, 1.65; P trend < 0.001). Subgroup analyses showed that pre-vitrification embryo grade acted as an effect modifier, with the positive association was more pronounced in transfers involving grade 3 poor-quality embryos (P for interaction = 0.018). No significant associations were observed between post-thaw cleavage progression and any short-term neonatal outcomes. Post‑thaw cleavage progression was significantly associated with increased live birth likelihood, with no significant associations with short‑term neonatal outcomes. Assessment of post-thaw cleavage progression may serve as a supplementary reference to support embryo selection in FET practice.