Embryo Assessment At The Post-Compaction Stage In The Ivf Laboratory

Limitations to embryo culture techniques in the early years of human in vitro fertilization (IVF) required transfer and/or cryopreservation of early cleavage-stage embryos on day 2 and day 3. Embryo quality scoring systems for these early cleavage-stage embryos were simplistic as the number of blastomeres, evenness of blastomere size, placement of blastomeres and extent of fragmentation were very evident. Extended culture of embryos to the blastocyst stage effectively doubled the time these embryos were maintained in vitro. Observations were commonly made at fertilization determination, mid-culture (day 3) and again at the end of the culture period (days 5 and 6). Evaluations of embryos on days 2 and 4 were then skipped in many laboratories. Qualitative selection protocols for morula-stage embryos rely on metrics associated with timing of compaction, extent of compaction, morphology of blastomeres and nuclei, extent of fragmentation and cavitation, if present. This chapter will touch on developmental details integrated into the suggested grading protocol, as well as providing evidence that morulae are overlooked as a viable clinical choice for transfer and for cryopreservation.