An embryo that has developed for five to six days after fertilisation is known as a blastocyst.

Development of an embryo to a blastocyst is a big step for a tiny new organism and makes it possible for more growth and change to come. Depending on how many embryos are produced after an IVF/ICSI cycle and their quality, embryos can be left in the laboratory for five to six days. 


With blastocyst transfer, embryos are allowed to develop to the blastocyst stage before they are transferred to the womb. Blastocyst transfer appears to increase the chance of a live birth, particularly for mothers under the age of 35. Unfortunately, when two blastocysts are transferred, it also greatly increases the risk of multiple births. It is thought that this is because only better quality embryos will survive for five to six days before transfer, so they are even more likely to implant themselves in the womb. It is at the blastocyst stage of development (five days after fertilisation) that an embryo would normally move out of the fallopian tube and into the uterus. Once in the uterus, the blastocyst starts to attach to the uterine lining in a process known as implantation.

The advantage of attempting to grow embryos to the blastocyst stage is that they should have a greater chance of implantation because the phase of embryo development matches the uterine environment.

If you and/or your clinician considers that that you are at risk of multiple pregnancy, you should discuss transferring only one embryo (single embryo transfer ), known as SET).


What might be the advantage of using Blastocysts culture and transfer?
• The ability to identify those embryos that are well developed and choose one of them for transfer. 
• More adequate synchronization of embryonic stage with the female endometrium. 
• Uterine contractions are reduced by day 5 thereby reducing the chance of an embryo being expelled. 
• The ability to undertake cleavage stage embryo biopsy which is easier and less harmful when the biopsy blastomere has to be taken.
• Increase implantation rate which need to transfer less number of embryos.
• Blastocyst stage embryos freeze as well, if not better, than cleavage stage embryos.

What might be the disadvantage of using Blastocysts for transfer?
• Patient may not have any suitable embryo remaining for transfer.
• Increase rate of monozygotic twins.


The possibility to grow the embryos to the blastocyst stage is offered to the following couples : 


  1. Patients with either a good response to gonadotropins  or with >4 eight-cell embryos on day 3. 

  2. If there is a need for embryo biopsy at the cleavage stage ( day 3 ) for genetic analysis. The embryo can then be cultured to the blastocyst stage without compromising its viability while the genetic tests are performed.

  3. Patients who are selected for one embryo transfer. (SET )

  4. Patients who had repeatedly failed IVF cycles to achieve a pregnancy following the transfer of good quality day 2 or 3 embryos (If the embryo arrested and did not develop to blastocyst, this may indicate a potential problem).

  5. Patient who do not wish to have their spare embryos frozen for whatever reasons may be advised to have blastocyst transfer for increasing ivf success rate.