Embryo transfer day 5 (blastocyst)
Since 2004, the Carl von Linné Clinic has been using the embryo scoring model on day 2. The model has allowed for the number of births per egg retrieval to remain the same but also dramatically decreased the risk of twins (please see under Science). Culturing the fertilized eggs a longer time to blastocyst (day 5) is used as an "extra selection instrument". In cases where there are several fertilized embryos, culturing them further to day 5 can increase the chance of choosing the right embryo to transfer.
All handling of fertilized eggs outside the body implies a risk for the embryo, so-called epigenetic changes. However, the concern about possible negative consequences of cultivation to blastocyst has proven unfounded. Previous reports of, for example, increased risk of malformations have not been seen in recent larger summary studies. In our own data, the outcome of blastocyst cultivation has also been very positive.
Blastocyst cultivation previously was only done as an exception. Because larger recent studies show good results and healthy babies, both in Sweden and internationally, we are now considerably less restrictive. Since 2014, we have progressively increased the number of blastocyst cultures and now use that method if we get plenty of eggs and good fertilization.
For further information, please see “What is blastocyst culture” under Results.