Blastocyst transfer allows selection of the best quality embryo(s) for transfer in the womb and therefore, it is recommended as a means of improving pregnancy chances.
What is blastocyst transfer?
Blastocyst-stage embryos have grown further, consisting of many more cells. Compared to the 2-3-day embryos, they have a thinner outer protective layer, or ‘shell’, which can ease their attachment, or implantation, to the uterine wall upon transfer.
While the majority of fertilized eggs, about 50%, will develop into a 3-day old embryo, only perhaps 40% of these embryos will develop into a blastocyst. These percentages become even lower in women older than 40 years of age. The embryos that do not make it to day 6, may bear a chromosomal or genetic defect, and if they had been transferred in the womb after 2-3 days, they would have failed to implant.
Therefore, allowing early embryos to reach the stage of blastocysts selects for the best embryos, the ones with a higher chance of establishing a pregnancy.
Who can benefit from blastocyst transfer?
Blastocyst transfer is beneficial for women that will have enough good quality embryos after IVF with or without ICSI. Ideally, if there are 3 or more embryos in day 5, the one(s) that have the best appearance, or morphology, will be selected for embryo transfer.
A blastocyst transfer is also beneficial for younger women with a good prognosis for pregnancy with IVF.
Additionally, blastocyst transfer may be a particularly useful option if there is a previous history of multiple pregnancy or a uterine anomaly, and if it is the personal choice of the patient to undergo an elective Single Embryo Transfer (eSET).
If you have experienced repeated implantation failure, extended culture of your early embryos allows us to examine their number and quality over a longer period. Identifying the percentage of embryos with halted growth or other abnormal characteristics may help to identify a potential problem. In these cases, culturing the embryos for 5 days, it also gives us the time to check for any genetic or chromosomal abnormalities with Preimplantation Genetic Diagnosis (PGD) and / or Preimplantation Genetic Screening (PGS).
How is blastocyst transfer done?
How does blastocyst transfer contribute to the success of assisted reproductive techniques?
Blastocyst transfer is associated with a high live birth rate. Waiting up to the blastocyst stage assesses the survival of the early embryo, which can be particularly advantageous for certain cases.
Normally, it is recommended that more than one embryo, either at the stage of 2-3 days or at the blastocyst stage, is transferred to the womb, as a means of increasing pregnancy chances. Research and experience have shown that in women under 35 years of age, single blastocyst transfer has the same success rate of a live birth as the transfer of more than one blastocyst. A single transfer can be a much safer option, as the risks of a multiple pregnancy are avoided. A single blastocyst, however, can still split after transfer leading to duplets.
In any case, you will discuss with your doctor about the number of embryos to be transferred, as this decision depends on many factors, including number of available embryos, their quality and your individual circumstances.
Despite the good results of blastocyst transfer, you need to remember that not all couples are eligible for it and that your particular history or situation may affect the outcome.