Once the sperm microinjects into the egg, the process of fertilization takes place. The fertilized egg develops into an embryo. If the embryo is mature enough, then within 3-5 days, we transfer it to the uterus; in some cases, we have to wait for six days.
Embryos reach the blastocyst stage on the fifth day. At this stage, the embryos are capable of attaching to the uterus.