Cleavage stage at compaction—a good predictor for IVF outcome

Objective: To analyze whether cleavage stage at compaction, and not only kinetics, can serve as a reliable predictor for clinical outcome. Methods: A retrospective cohort study including 1194 embryos, classified by compaction initiation stage (Group 1: compaction at fewer than eight cells, Group 2: compaction at eight cells, Group 3: compaction at more than eight cells). Of these, 815 embryos were evaluated for morphokinetic preimplantation parameters, and 379 embryos were analyzed for clinical implantation following thawing and transfer of single blastocysts during the same period. Results: In total, 1194 embryos were analyzed. Embryos that underwent compaction from more than eight cells (Group 3) exhibited more synchronous cleavage compared with Groups 1 and 2 (at both S2 and S3; P < 0.001), and displayed a significantly lower fragmentation rate. The likelihood of obtaining top-quality blastocysts decreased by 73% and 44% when comparing Group 3 embryos with those of Groups 1 and 2, respectively, (P < 0.03). Clinical validation of the results shows that while compaction from fewer than eight cells barely produced blastocysts for transfer, compaction at eight or more cells is crucial for implantation and birth (birth rates 11.1% and 18.5% for Groups 2 and 3, respectively). Conclusion: Cleavage stage at compaction has a direct effect on blastocyst quality and subsequent pregnancy, so can be included in newly developed deep learning models for embryo selection.