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In most IVF cycles at Reproductive Biology Associates the embryos are transferred on day 3, at around the 8 cell stage. We have found that this gives excellent success rates and limits the time the embryos are outside the body. In some cases however, we may recommend a blastocyst transfer. A blastocyst is is an embryo that has developed so that by day 5 it has turned into a hollow ball of cells, and is ready to expand, hatch out of the zona pellucida and implant into the uterus.
Advantages of blastocyst transfer
- Blastocysts that are transferred on day 5 synchronize with the time that embryos will usually reach the uterus in a natural conception. The uterine environment is quite different to that of the fallopian tubes and as the embryos are transferred to the uterus, it is thought it could be an advantage to wait until the blastocyst stage for this reason.
Embryos that reach the blastocyst stage have proven themselves to have a strong developmental potential, in addition using our grading system we can select the best blastocysts to transfer and hence we will not need to transfer as many embryos. Blastocyst transfers can help to reduce multiple order pregnancies.
Disadvantages of blastocyst transfer- Not all embryos make it to the blastocyst stage and one reason for this is that the culture media used so that embryos can reach this stage outside of the body is still not optimal. This means that there could be some embryos that would do better if transferred to the uterus sooner, rather then waiting until day 5.
- Fewer embryos are frozen at the blastocyst stage.
Some indications for blastocyst transfers- Previous failure of good quality embryos to implant
- Preimplantation genetic diagnosis
- Reducing risk wish to a multiple pregnancy.
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