A blastocyst is an embryo that has developed for five to six days after fertilisation.
With blastocyst transfer, embryos are cultured in the incubator to the blastocyst stage before they are transfered to the womb.
At this time, one or two of the best quality blastocysts are selected and then transfered into the woman's womb. A blastocyst must successfully attach itself to the wall of the womb for a woman to become pregnant.
The procedure for blastocyst transfer is similar to that for normal embryo transfer, but instead of being transfered into the womb after two or three days, the embryos are allowed to develop for five to six days at the laboratory before transfer.
Not all embryos will develop to blastocysts in the laboratory. Embryos can stop developing at the four-cell stage (day two) and progress no further.
As with normal embryo transfer, due to the risks of a multiple birth if more than one blastocyst is transfered, you may want to consider single blastocyst transfer.