Blastocyst culture and transfer
A blastocyst is a fertilised embryo that is five or six days old. Historically embryo transfer following IVF or ICSI takes place two or three days after egg collection when the embryo contains around six to eight cells. However, with improvements in culture media we can now culture embryos for five or six days more successfully than in the past. By this stage the embryos have numerous cells (approximately 80 – 100) and start to form two distinct layers. The embryos are then known as blastocysts and it is at this stage in nature that spontaneously conceived embryos start to implant in the womb.
Culturing embryos to day four or five enables the laboratory to assess the development potential of the embryos. By doing this we can select the embryo for transfer which have the best chance of pregnancy. This selection process is most beneficial when we have several fertilised eggs. We would then culture the embryos to day four or five and select the best for blastocyst transfer.
Unlike a day three embryo which must develop further once it has been transferred, an embryo that reaches blastocyst stage in the laboratory only has to implant once it has been transferred. Results show that blastocyst transfer success rates are higher than the transfer of day three embryos.
Blastocyst culture at the LWC
The London Women’s Clinic now uses blastocyst culture as part of its standard laboratory procedures. The day after egg collection an embryologist will call to discuss the fertilisation rate and when transfer may take place. This will normally now be on day five or six following egg collection but in some circumstances could be on day three. In some instances, all embryos may be frozen for transfer at a later date.