Human embryos from in vitro fertilisation in culture in an IVF lab usually reach blastocyst stage by day 5 after fertilisation.
Blastocyst is an embryo which has developed to day 5 stage with different cell components and a fluid cavity.
At blastocyst stage of development, the embryo must reach before it can implant in the uterus.
Blastocyst embryos have the best potential for implantation.
Blastocyst culture offers single embryo transfer and significantly reduce the risk of multiple pregnancy.
Blastocyst culture can help to determine which embryos have the best chance of being able to implant.
Extended culture allows the embryologist to identify which of a group of embryos have the best potential for implantation.
If IVF does not work repeatedly with good embryos replaced on day 2 or 3, blastocyst culture can be tried.
Extended culture allows the embryologist to identify which of a group of embryos have the best potential for however the chances of having no embryos for transfer at all are also higher.
Transferring embryos at the blastocyst stage also provides a better co-ordination between the embryo and the uterus by putting the embryo back in the uterus at the right time.