An embryo that has progressed to a stage where it begins to form a fluid-filled core is called a blastocyst. This is a critical part of embryo development which usually occurs five to six days after ovulation. Blastocyst transfer is the placement of blastocysts into the uterus.
Most women would not be having a problem getting a transfer with embryos that have progressed to the blastocyst stage. But it’s is not suitable for all women. The day of embryo transfer depends on the number and quality of embryos available on the third day after the eggs are harvested from the woman. A woman is likely to have blastocysts two days later if she has four or more high quality embryos on the third day after egg harvest. If the woman is older than 35, or has few high quality embryos on the third day after transfer, she is less likely to have blastocysts two days later. A day-three embryo transfer is often more appropriate for these women.