IVF- Blastocyst Transfer

IVF patients undergo drug stimulation with follicle stimulating hormone to cause the recruitment and development of numerous eggs. These eggs are needed for fertilization with the partner's sperm. Once the eggs are fertilized, they are placed in incubators where they remain until ready for transfer to the mother's uterus.

The embryologist and physician closely monitor the embryos in culture while they divide and develops to maturity, usually within three to five days. Until recently, the culture media that was used only supported growth of the embryo up to three days; therefore, most embryo transfers were performed on day three. Culture media is now more advanced and able to support the growth of embryos up to day five, to the blastocyst stage.

A blastocyst is an embryo, which has developed two cell types, 1) surface cells termed the trophectoderm, which will become the placenta and 2) the inner cell mass that will become the fetus. A healthy blastocyst should hatch from its shell (zona pellucida) by the end of six days, or earlier, and implant within the endometrium.

The benefit of a day five transfer is that it allows the embryologist to watch the embryo for a longer period and more realistically assess it's quality. Embryos that appear good quality on day three may not survive to day five and embryos that do not appear good quality on day three may divide well up to the blastocyst stage. If an embryo does survive up to day five, it has a better chance of implanting than a day three embryo so fewer need to be transferred to the uterus. The major advantage of a day five transfer is transferring fewer embryos and a decreased risk of high order multiple births.

The couple must have enough embryos to make blastocyst transfer feasible. For example, if a couple only has 2-3 embryos they will typically all be transferred on day three. If however there are >= eight embryos, it would benefit to choose the best ones and the embryo transfer may be performed on day five.