Embryo Freezing (Vitrification) and Frozen Embryo Transfer (FET)
Embryo Freezing (Vitrification)
The embryos can be frozen and stored at a low temperature for future use just as with sperm and oocytes. In order to carry out this embryo storage, a procedure of embryonic freezing has to be done. The old way of embryo freezing didn’t have good successful rates of implantation. But now the best technique in the world is vitrification. The new, advanced method known as Embryonic Vitrification offers greater effectiveness in survival of the embryos as well as a better rate of implantation, clearly increasing pregnancy rates. Vitrification cools the cells in an extraordinarily fast way, unlike the classic freezing process. The liquid therefore does not have time to form crystals. Therefore there is no damage to the embryos caused by ice crystals which are formed during the slow freezing technique. In the past, they were slowly cooled in order to avoid the water surrounding and inside the embryos becoming ice. However, vitrification cools the cells immediately at a speed greater than 15.000º C per minute so that there is no time for ice to be formed, but instead a kind of gel appears leaving the cells undamaged. Thus, we can ensure that fewer embryos are damaged and can provide better rates of implantation. Now by using vitrification, more than half of them achieve pregnancy.
Frozen Embryo Transfer (FET)
You may do a frozen embryo transfer (FET) cycle, if you have frozen embryos and wish to use them. This may be after a successful IVF cycle and the delivery of a child, and you wish to come back and use your frozen embryos. It could also be after an unsuccessful stimulated IVF cycle, in which you have obtained frozen embryos.
The benefits of a frozen embryo transfer (FET) over a fresh (stimulated) cycle include lower cost, less complex treatment (e.g. no surgical retrieval of eggs), less medication, and generally similar success rates.
The success rates of an FET are nearly the same as fresh IVF cycles.
FETs use blastocysts or embryos day 3 that have been frozen following a fresh cycle.
At cycle baseline, patients are instructed to begin estrogen, to build the uterine lining. At ‘lining check,’ upon demonstrated of a thickened endometrium, patients are instructed to add in progesterone. A frozen embryo transfer date is confirmed, and the patient presents for her frozen transfer.
Estrogen and progesterone continue during the frozen transfer, and through the blood pregnancy test, about two weeks later.
Most patients will be on a cycle/month of oral contraceptives (birth control pills) before their actual frozen cycle.
An average patient may have 3 appointments during her cycle. One for a baseline evaluation (blood and vaginal ultrasound), before her medications are started. 2ndat mid-cycle (‘lining check’), to insure the uterine lining is thickened, and 3rd on the transfer appointment itself. Then a beta HCG pregnancy test two weeks later will be done.