PREDICTION OF THE DEVELOPMENTAL POTENTIAL OF HAMSTER EMBRYOS IN-VITROBY PRECISE TIMING OF THE 3RD CELL-CYCLE

Time-lapse videomicrography was used to determine the timing of early developmental events in hamster embryos in vitro. The time intervals f rom pronuclear envelope breakdown to the completion of the first cleav age (Dt(2)), second cleavage (Dt(4) = 2-4 cells), third cleavage (Dt(8 ) = 4-8 cells), blastocyst formation, and zona escape were precisely m easured to determine whether the variable 'time' (t) can be used to pr edict the developmental potential of preimplantation embryos. The rang e of the developmental time interval (Dt) from the second to the third cleavage divisions (Dt(8)) provided the best indicator for predicting the probabilities of blastocyst formation and zona escape (P = 0.015 and 0.041, respectively). Dt(8) was subdivided into consecutive time c utoff points of less than or equal to 750, less than or equal to 800, less than or equal to 850 and less than or equal to 900 min. Of the em bryos that took less than or equal to 750 min to complete the third cl eavage division, 92% developed into blastocysts and 69% escaped from t heir zonae pellucidae. When the completion of Dt(8) extended to less t han or equal to 900 min, the percentages decreased to 75% and 49% for blastocyst formation and zona escape, respectively. This study identif ies a specific developmental time interval and a model whereby time ta n be used as a noninvasive parameter to predict embryo developmental p otential in vitro.