In standard IVF, embryos are grown under very strictly controlled conditions in the laboratory for two or three days. They are then transferred into the woman’s uterus (womb) and any additional embryos can be frozen for future use. Blastocyst culture refers to growing the embryos in the laboratory for two more days at which point they are referred to as blastocyst embryos. Blastocyst transfer simply means that the blastocyst embryos are transferred to the woman’s uterus on day 5 in exactly the same way that day 3 embryos are.