ABSTRACT
INTRODUCTION Blastocyst vitrication is now a routine procedure that allows patients to store high-quality embryos indenitely with a high expectation of pregnancy post-warming.1 Patients with multiple blastocysts will routinely transfer just a single fresh embryo (elective single-embryo transfer) to avoid multiple pregnancy,2 with the knowledge that their remaining embryos can be successfully frozen and stored until needed. At the time of warming, it will again be ideal to use just a single embryo from the freezer to maintain the eciency and safety of the process, particularly in younger patients, those who experienced a loss or miscarriage aer a previous transfer, or if the embryo is known to be euploid aer chromosome analysis.3 In attempting to use a single embryo and to give the patient the greatest possible chance of pregnancy, the embryologist is charged with recovering, warming, and culturing the embryo, and with accurately assessing the viability of the embryo before transfer. In addition, the embryologist needs to be aware of procedures that may limit or enhance the embryo’s chance of implantation,4 such as timing of warming and transfer relative to uterine receptivity,5 culturing the embryo for an appropriate time before transfer, and assisted hatching (AH).6
