Prediction of the developmental potential of hamster embryos in vitro by precise timing of the third cell cycle

Time-lapse videomicrography was used to determine the timing of early developmental events in hamster embryos in vitro. The time intervals from pronuclear envelope breakdown to the completion of the first cleavage (Dt2), second cleavage (Dt4 = 2-4 cells), third cleavage (Dt8 = 4-8 cells), blastocyst formation, and zona escape were precisely measured to determine whether the variable 'time' (t) can be used to predict the developmental potential of preimplantation embryos. The range of the developmental time interval (Dt) from the second to the third cleavage divisions (Dt8) provided the best indicator for predicting the probabilities of blastocyst formation and zona escape (P = 0.015 and 0.041, respectively). Dt8 was subdivided into consecutive time cutoff points of < or = 750, < or = 800, < or = 850 and < or = 900 min. Of the embryos that took < or = 750 min to complete the third cleavage division, 92% developed into blastocysts and 69% escaped from their zonae pellucidae. When the completion of Dt8 extended to < or = 900 min, the percentages decreased to 75% and 49% for blastocyst formation and zona escape, respectively. This study identifies a specific developmental time interval and a model whereby time can be used as a noninvasive parameter to predict embryo developmental potential in vitro.