Late stages of embryo progression are a much better predictor of clinical pregnancy than early cleavage in intracytoplasmic sperm injection and in vitro fertilization cycles with blastocyst-stage transfer.

Objective: To define and validate metrics of embryo progression and morphology during extended embryo culture and to compare the effects of early cleavage (EC) vs. blastulation stages on clinical pregnancy.

Design: Retrospective observational study.

Setting: University-affiliated assisted reproduction center.

Patient(s): One thousand two hundred ninety-two intracytoplasmic sperm injection and 842 IVF blastocyst-transfer cycles.

Intervention(s): The embryo progression index (EPI) was calculated as the area under the curve of total cell number (TCN) over time, by using observed TCN for cleavage-stage embryos and estimated blastocyst TCN according to morphology. The EPI from days 1-3 measured early cleavage, and blastulation was assessed by EPI over extended embryo culture. Blastocyst morphology was converted into numerical blastocyst quality scores (BQSs). Receiver operating characteristic curve analysis was used to evaluate predictors for clinical pregnancy.

Main Outcome Measure(s): Clinical pregnancy.

Result(s): Per-cycle mean EPI and mean BQS for all embryos developing into blastocysts, as well as mean BQS of the transferred embryos, were significant predictors of clinical pregnancy in intracytoplasmic sperm injection and IVF cycles. Mean EPI for days 1-3 did not predict outcome.

Conclusion(s): Early cleavage is a putative marker of embryo quality. Late-stage embryo development is more sensitive and specific in predicting clinical pregnancy than is early cleavage, supporting the use of extended embryo culture for embryo selection. The embryo progression index and BQS may also be used for this purpose.