A frozen embryo transfer, or FET, is a kind of IVF treatment where a cryopreserved embryo created is thawed and transferred.
“Extra” embryos may result after an IVF cycle. Rather than wasting them, people choose to freeze or cryopreserve them. Multiple embryos resulting in twins, triplets, quadruplets, etc. are not recommended and the doctor recommends elective single embryo transfer for you. This means that a single embryo will be transferred while the extra ones will be cryopreserved.
In case the transferred embryo results in unsuccessful pregnancy, you can choose to go through a fresh IVF cycle or transfer the cryopreserved embryos. This is a more cost-effective option in such a case.
Preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS) help identify any genetic disease in an embryo. Post egg retrieval, the embryo is biopsied, helping to get back results in time to do a fresh embryo transfer. If a biopsy is done on or after the fifth day, due to the complexity involved, it requires more time, and this becomes the reason for embryos under the screening process to be cryopreserved. Results can help make the decision on which embryos to transfer, resulting in a FET.
If you have conceived a child through IVF and chose to cryopreserve the extra embryos, you can use these embryos for another pregnancy. Choosing to use the cryopreserved embryos rather than fresh embryo transfer is more cost-effective as the latter one is a more expensive route.
If your fresh embryo transfer is unsuccessful, frozen embryos from previous cycle may be used to try against without using ovarian stimulation medication or having another egg retrieval operation.
After the initial IVF treatment cycle, the following FET cycles are less heavy on the patient’s wallet. Medication and treatment, both cost much lesser than a fresh embryo cycle. Lesser monitoring visits, no egg retrieval, insemination, or embryo culture also reduces the treatment cost by a great margin.
FET cycles are easier as they do not require surgery or anesthesia for egg retrieval. Initially, estrogen injections are used to prepare the uterine lining and are administered only once every three days. Intramuscular progesterone is added later in the cycle which is required daily.
OHSS has less than 1 percent chance of occurring but if potential warning signs are seen by a physician that the woman is at high risk for OHSS, they may recommend freezing of all available embryos rather than a fresh transfer, due to pregnancy increases the risk of OHSS. The embryo can later be safely transferred through FET.
After egg retrieval and fertilization, the embryologist may biopsy each suitable embryo on day 5 or 6 of development. Rather than proceeding with transfer right away, the embryologist will freeze the embryos while awaiting results against Preimplantation genetic diagnosis (PGD) for genetic mutations. The embryos to be transferred can be screened and only embryos in which genetic mutation in question is absent may be used.
Embryo freezing also allows for preimplantation genetic screening (PGS). PGS looks for irregularities in chromosome number, e.g. trisomy 21, which causes Down’s Syndrome, and other such abnormalities that may result in implantation failure or miscarriage.
Lesser chances of stillbirth, preterm birth, and low birth weight were observed in FET over the fresh embryo cycle.
Embryos transferring may result in a risk of multiple pregnancies, which come with an increased risk for both mother and child. A small risk of infection is also present. With cryopreservation, the freezing and thawing process may result in the loss of some embryos even after the screening, which might result in you losing an embryo which might have been present with a fresh transfer. FET might also increase the risk of “large for gestational age” babies.