Purpose: To demonstrate whether the standard morphokinetic markers used for embryo selection have a similar relationship to blastocyst formation and implantation in two large clinical data sets.
Methods: This is a retrospective cohort analysis striving to answer two distinct questions utilizing data sets from two large IVF clinics. Blastocysts (BL) and implanted blastocysts (I) in both clinics, IVI-Valencia (BL = 11,414, I = 479) and WMC (BL = 15,902; I = 337), were cultured in a time-lapse system (EmbryoScope, Vitrolife, Sweden). The study was designed to assess the relationship between early morphokinetic hallmarks and BL development, with a secondary analysis of implantation rates following single-embryo day 3 and day 5 transfers.
Results: We performed a detailed graphical analysis for t3, t5, duration of the second cell cycle (cc2) (t3-t2), and the ratio (t5-t3)/(t5-t2). The t5 timing was not affected between the clinics. However, Weill Cornell Medicine's (WCM) proportions were significantly affected by having BL vs. not. A significant decrease of blastocysts with longer t5 in WCM data, while t5 was more informative in the IVI data set for the implantation rate.
Conclusions: Morphokinetic intervals for early cleavages were distributed differently between the clinics. Incorporation of embryo-selection algorithms depends on the individual clinic's selected developmental hallmarks, all of which must be validated before incorporation into clinical practice.
Keywords: Embryo selection; Implantation rate; Morphokinetics; Time-lapse incubator.