Compaction timing but not its magnitude predicts the clinical potential of human IVF embryos

Research question: How to objectively quantify compaction magnitude and timing to help determine the clinical potential of in vitro fertilization (IVF) human embryos?   Design: We retrospectively analyzed 79 time-lapse movies of high-grade transferred human blastocysts, to quantify compaction, measuring blastomere contact angles and recording the timing of compaction and blastocoel formation. Contact angles, developmental timing, clinical data, standard embryo quality assessment, clinical pregnancy and live birth were analyzed using multivariate general linear models.   Results: Most high-grade blastocysts (64/79) have finished compaction during or after the 16 cell-stage. We measured a mean angle of compaction at 151.5° ± 1.1 regardless of the embryo cell developmental stage at compaction. No difference in the contact angle nor the embryo cell-stage at compaction between implanted (n=19) and non-implanted (n=60) embryos was evidenced. Implanted embryos compacted 5.2 ± 1.9 h earlier than embryos that failed to implant (p = 0.025). No association was found between compaction parameters and patient or ART characteristics. Conclusion: Our study provides a simple and objective approach to quantify compaction and suggests that the timing of compaction, but not the embryo developmental stage it occurs nor its magnitude, is a relevant parameter to consider when selecting the blastocysts to transfer.