The development of the early embryo
The embryo arises over the course of the first day from the fertilised ovum through the fusion of the mother’s and the father’s pronuclei. The embryo begins to divide and under optimal conditions it reaches the four-to-eight cell stage after two or three days. In the following days, the embryo then significantly picks up speed: On the fifth day, it consists of over 60 to 100 cells and is in what is known as the blastocyst stage.
The blastocyst culture
The second or third day of embryo development has proven to be a good time for the embryo transfer in IVF or ICSI treatment. Due to medical progress, it has become possible to cultivate embryos for five days until the blastocyst stage.
The later replacement of embryos on day five makes it possible to observe the development of the embryos for longer. Due to the longer time between ovum collection and embryo transfer, the body additionally has more time to recover from the hormonal treatment. A blastocyst thereby often has a higher probability of implanting and thereby leading to a pregnancy.
Blastocyst cultivation is most frequently carried out when many fertilised ova are available. If an embryo reaches the blastocyst stage, then the protective shell (which is known as the zona pellucida) that surrounds it is very thin. The assisted hatching procedure is therefore not carried out on embryos in the blastocyst stage. In the case of ova that were cryopreserved, a blastocyst cultivation is also possible, but is only rarely carried out.
The blastocyst culture increases the change of a successful pregnancy.
A blastocyst has a higher probability of implanting (about 35%) and thus leading to a pregnancy than an embryo in an earlier stage.
Due to the high probability of pregnancy after the transfer of embryos in the blastocyst stage, normally only one or two embryos are transferred. Triplet pregnancies can thus be almost completely excluded and twin pregnancies can be significantly reduced.
Unfortunately, only about a third of all fertilised ova develop into a blastocyst.
When setting up the embryo culture according to the so called "Deutscher Mittelweg", several oocytes can by taken into culture. On the day after the follicle aspiration, the number of oocytes that are necessary to yield the desired number of embryos on the chosen transfer date is calculated. Should there be any excess embryos at the day of the transfer, those have to be cryopreserved.
Generally, the additional costs of a blastocyst culture are not paid by the statutory health insurance companies.
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