Culture to blastocyst
The long culture of embryos in an in-vitro fertilisation cycle allows them to develop to the blastocyst stage.
As only the best embryos reach blastocyst stage, the transfer is carried out on the fifth day– instead of on the second or third, which is the usual time – thereby allowing a greater selection, which means an increase in the pregnancy rates and a reduction of the risk of multiple pregnancy.
In natural conception, it is precisely the fifth or sixth day after fertilisation when the embryo comes into contact with the endometrium (uterus lining), which leads to pregnancy. Transferring the embryos as blastocysts promotes the natural synchrony between the embryo and the material uterus.
This technique is indicated in:
- IVF Cycles with a reliable number of embryos in excess of the number of embryos that would be transferred and where the embryo quality is very similar and does not allow differentiating the most apt for transferring and leading to pregnancy.
- Cases of repeated implementation failure
- Cases of Pre-implementation Genetic Diagnosis, where the long culture is essential for keeping the embryos in culture until the results of the analysis are obtained.
On the other hand, the long culture is not a technique suitable for the other cases, because it involves the risk that the embryos do not reach the blastocyst stage in the laboratory and, therefore, the transfer cannot be carried out.
At present, the improvements in the culture media and the technological advances in IVF laboratories have increased the efficiency of the culture to blastocyst stage, and so it can be used routinely.