Day 3 morphology is a poor predictor of blastocyst quality in extended culture

Objective: To determine how the quality of blastocysts formed on day 5/6 of extended culture compares with their morphology on day 3. Design: Retrospective observational study of IVF laboratory records. Setting: Private assisted reproduction clinic. Patient(s): 101 IVF cycles in which 5 to 25 embryos were produced. The average maternal age was 33.1 years. Intervention(s): Embryos were individually cultured in vitro in sequential media for an extended time to enable use of blastocysts for fresh transfer or cryopreservation. Main Outcome Measure(s): Comparison of embryo quality for putative ET or cryopreservation on day 3 with quality of embryos used for actual ET and cryopreservation on day 5/6. Result(s): Of 1,263 cleaving embryos, 559 were judged to have been suitable for use on day 3; 355 would have been used for ET (average per ET, 3.5) and 204 would have been frozen (equivalent to 44% utilization). In actuality, 471 blastocysts were used on day 5/6, of which 234 were transferred (average per ET, 2.3), and 237 were frozen (equivalent to 37% utilization). Only 48% embryos that would have been chosen for ET and/or cryopreservation on day 3 were eventually used in such a manner at the blastocyst stage. Historically, the rate of viable pregnancy from day 3 transfers was 30.5% per transfer; this rate increased to 45% with routine day 5/6 transfers. Conclusion(s): Extended culture of human embryos seems to increase discrimination of potential embryonic viability. Criteria for embryo selection on day 3 seem to be inadequate. Extended in vitro culture may therefore be an effective means of optimizing IVF clinical success. (Fertil Steril(R) 2000,74.495-7. (C) 2000 by American Society for Reproductive Medicine.).