In most laboratories, embryo transfer traditionally takes place on day 2 to 3 of culture, or during blastocyst stage, whilst embryo transfer on day 4 is an alternative that has not commonly been adopted into laboratory practice.
When compared with embryo transfer during early stages, blastocyst transfer is generally accepted as superior. This is mainly for reasons of improved synchronisation between the embryo and the endometrium and more objective embryo selection once the genome has been activated. It means that a smaller number of embryos can be transferred, thus avoiding the risk of a multiple pregnancy. […]