A frozen embryo transfer cycle is a procedure using cryopreserved embryos from a previous IVF treatment. Embryos are frozen with a very specialized technique that is designed to minimize the risk of damage to embryos. Once embryos are frozen, they are stored in liquid nitrogen. While stored in liquid nitrogen, the cells do not age or deteriorate. This allows embryos to be frozen for any length of time and retain their ability to make a pregnancy years later. In the past, techniques used to freeze the embryos resulted in a slight reduction in the chances of pregnancy. With a modern technique called vitrification, the embryos are frozen in such a way there is minimal risk of ice crystal formation within the embryos. Vitrification allows for excellent survival during the freezing and thawing process.
Improvements In Pregnancy Rates
Older methods of freezing embryos resulted in pregnancy rates that were slightly lower than rates achieved with fresh transfers. After California IVF was able to fine tune the vitrification process, the success rates with frozen embryo transfer cycles were found to be significantly higher than the fresh transfer pregnancy rates. Obviously the freezing process does not improve the embryo quality. It is believed that the process of stimulating the eggs to grow is causing the lining of the uterus to become less favorable. This has led to a new era in IVF. Collecting the eggs and forming embryos is performed similar to before. Instead of proceeding with a fresh embryo transfer, embryos are frozen at the blastocyst stage (day 5 or day 6 embryos). The uterine lining is allowed to recover and the patient undergoes a frozen embryo transfer, or FET cycle. This allows for a 15 to 20% improvement in pregnancy success for most patients. Changes in the approach to fresh and frozen embryos and the way fertilization and embryo culture is performed is just one example of how California IVF Fertility Center ischanging the way fertility treatments are performed.
The FET process is easier and more predictable than a fresh IVF cycle. During the frozen embryo transfer process, the uterus is prepare to receive the embryos which are thawed on the day of the embryo transfer.
Embryos frozen from previous IVF do not have a shelf life and can be used years after the initial IVF cycle from which they were produced. Couples having a successful IVF treatment can return several years later and have an FET cycle done for far less cost than IVF. Time does not affect the ability of the embryos to make a pregnancy so it is even possible to return to the clinic 10 or more years later and have embryos transferred that were formed from the eggs collected when the woman was much younger. This is a variation of fertility preservation and is a benefit of in vitro fertilization (IVF)
The hormonal treatment in a FET cycle involves down regulating the ovaries with a medication such as Lupron. You then take estrogen to build up the lining of the uterus. Estradiol patches are our preferred way of providing the estrogen. Several days prior to the transfer of the embryos, you will stop Lupron and begin taking progesterone. Progesterone is typically givn by progesterone in oil injections or vaginal suppositories. The timing of these hormones coincide with the hormone changes seen with ovulation. By mimicking the normal hormone changes of the menstrual cycle, the embryo transfer can be synchronized to match the stage of the frozen embryos. The embryos are thawed on the same day they are transferred into the uterus. A pregnancy test is done approximately between 8 and 10 days later.
Not all embryos survive the freezing and thawing process. We attempt to thaw the embryos in a manner that we can get the desired number for transfer while keeping any extra embryos frozen. Often times couples may have a lot of embryos but they must all be frozen in an effort to get 1-2 good quality embryos for transfer. We are happy to discuss FET and cryopreservation if you have any additional questions.