If there is more than one good high-quality embryo in an IVF-treatment, the ones that are not transferred will be frozen in liquid nitrogen by -196⁰C. The embryos can later be thawed and transferred, either in af unstimulated/spontaneous cycle or in a hormone stimulated cycle.
We only freeze embryos, that have developed to blastocysts (have been cultured in 5-6 days).
Even though we are only freezing high-quality blastocysts, not all of them are surviving the freezing and thawing. In average 90% of the blastocysts survive the thawing.
The frozen blastocysts have to be destructed if the couple separates, or one of the parties dies. It can be agreed among the parties, that if the male part dies, the female part can use the frozen blastocysts. (The agreement must be written).
If the blastocysts origins from a treatment of a couple:
- Both parties must consent to the freezing and storing of the blastocysts in writing.
- The blastocysts can only be thawed and used, if both parties give their consent in writing before the thawing and transferring of the blastocysts.
The pregnancy rate after Frozen Embryo Transfer (FET) is 30-40%.
For women with regular cycles within 35 days, the thawed blastocyst is transferred in a normal cycle (unstimulated).
If a cycle is long (more than 35 days) or irregular, the endometrium is primed to receive the blastocysts, by using tablets or bandaids containing Estradiol (stimulated cycle).
Transferring thawed blastocyst in an unstimulated cycle
Transfer of thawed blastocyst is often done without hormone stimulation.
Once your period starts, you must call the clinic, to make an appointment for a scan of the endometrium day 10-12 in your cycle. The scan determines the thickness of the endometrium, and the size of the follicle.