A frozen blastocyst transfer is an embryo transfer that involves transferring one or more embryos that are at a very advanced stage of development, called the blastocyst stage. This is usually done on the fifth day after follicular aspiration.
After the doctor has removed the eggs from an ovary (follicular aspiration), they are fertilised in the laboratory. This is done either by normal in vitro fertilisation (IVF) or by means of intracytoplasmic sperm injection (ICSI).
Immediately after fertilisation, an egg starts to divide and develop into an embryo. The stages of development are as follows:
Day 1: The pronuclear stage (fertilised egg)
Day 2: Two- to four-cell stage
Day 3: The eight-cell stage
Day 4: The morula stage
Day 5: The blastocyst stage
The embryos can also develop in an incubator up to the fifth day, i.e. the blastocyst stage, thanks to improved cell culture media (blastocyst culture). If the doctor transfers such developed embryos into the woman’s uterus, this is referred to as blastocyst transfer.
It is possible to identify embryos with development potential
Only 20 to 30 percent of the fertilised eggs develop into blastocysts at all. If an embryo reaches this stage, there is a higher chance of implantation.
The moment of blastocyst transfer is ideal
Just like with a blastocyst transfer, in a natural pregnancy, it takes around five days after fertilisation for the embryo to reach the uterine cavity, where it then implants. It is assumed that the lining of the uterus is particularly receptive on this day.
In Germany, under the Embryo Protection Law, a maximum of only three fertilised eggs is allowed to mature to the blastocyst stage in an incubator. In addition, the German Embryo Protection Law prohibits the selection of embryos.
A decision on which of the fertilised eggs will be suitable for a blastocyst transfer is made during the first day after fertilisation, in the pronuclear stage. During this stage, the nuclei of the egg and sperm cells are not yet fused together. At this point, these cells are not yet embryos. Excess fertilised eggs in the pronuclear stage can be frozen (cryopreservation).
The chances of getting pregnant after blastocyst transfer are very high. Compared to embryo transfer at an early development stage (day 2 or 3), the odds are increased by around seven percent (Source: DIR Jahrbuch – German IVF-Registry Annual 2014). In women up to the age of 30, the chance of success is between 45 and 50 percent, and for women aged 30-39 it is between 35 and 40 percent.
However, blastocyst culture does not provide the same advantages for all women. Those with a low egg count and quality may indeed benefit from a day-3 transfer, in which the embryos are inserted in the mother’s uterus at an earlier stage. It, therefore, goes without saying that our reproductive medicine specialists will work together with you to determine the best transfer method for you as part of a personalised individual medical approach for the best possible chance of success.