Frozen Embryo involves a procedure where the embryos are frozen after fertilization and subsequent growth. The embryos may be frozen between day 2(four-cell stage) – day 5 (blastocyst stage). Healthy and viable embryos are moved to a ‘freezing machine’ where the temperature is made to drop rapidly to MINUS 150 degrees Celsius and then stored in liquid nitrogen tanks at -196 degree Celsius.
A frozen embryo transfer (FET) is a part of IVF treatment, where a cryopreserved embryo, created in an l IVF cycle, is thawed and transferred to a uterus. The process involves preserving an embryo at -150 Celsius temperature, generally at an embryogenesis stage, corresponding from fertilization to the blastocyst stage. A cryopreserved embryo can also be a donor embryo or may have been ‘prepared’ from a donor egg or donor sperm.
In principle, most IVF cycles involve frozen embryo transfers. Fresh embryo transfers are rare. This is because the techniques of FET have improved a lot and the outcome of FET is much better than fresh transfers. Most doctors recommend elective frozen embryo transfer (also referred to as a “freeze all” approach) where a fresh embryo transfer is not opted. Here all the embryos are cryopreserved and transferred in the FET cycle in the next month or so.
Depending on the woman’s health conditions and some circumstances, the fertility doctor may advise FET that will help the woman get pregnant now or anytime later in future. A Frozen Embryo comes with a lot of benefits:
Several embryos can result from the IVF cycle. Transferring of multiple embryos into the uterus increases the risk of high-order multiple pregnancies (like triplets or quadruplets). To reduce this risk, the doctor might recommend an elective single embryo transfer (eSET) to have a good and safe pregnancy. One can choose to freeze or cryopreserve any “extra embryos” after their IVF cycle.
The cryopreserved embryos are of use when a fresh IVF transfer fails. For instance, let’s say you get five embryos from the IVF cycle and your doctor recommends elective single embryo transfer as a fresh embryo transfer. One among the five IVF embryos is transferred into the uterus. The remaining four are cryopreserved. If the embryo transfer doesn’t result in a successful pregnancy, the womanhas two options. She can opt for another full IVF cycle, or can transfer one or two of the cryopreserved embryos. The most cost-effective option would be to transfer one or more embryos from the preserved frozen embryos or the cryopreserved embryos.
Cryopreserved embryos can remain on ice indefinitely. If the couple decide to give their IVF-conceived child, a sibling and if they still have embryos in cryopreservation, those cryopreserved embryos could help attain pregnancy again. The couple don’t have to repeat the whole IVF process.
Screening embryos for specific hereditary disease or defects is possible using PGD and PGS. It is done through a biopsy on day three or five post-fertilization, post egg retrieval. PGD and PGS help reduce the risk of passing genetic diseases. This can only be done if the embryos are frozen.
FET is an integral part of pre-implantation genetic testing (PGT). All embryos biopsied are cryopreserved. Once the results come, the doctor can decide which embryos to transfer for the FET-IVF cycles, based on the results of the PGT.
The woman can opt for an elective frozen embryo transfer with or without PGD/PGS. With the “freeze all” approach, the fresh embryo transfer is not a part of the plan. It can occur with PGD/PGS or without genetic screening. A Fresh Embryo Transfer might be less likely to result in a viable, healthy pregnancy. To avoid this and to be safe, all embryos are cryopreserved three to five days after egg retrieval. After a month, there is a chance of endometrium to form without the influence of ovarian stimulating drugs, when frozen embryo transfer can take place. During that FET cycle, the fertility doctor may prescribe hormonal medications to enhance endometrial receptivity (especially if the woman does not ovulate on her own, doctor might do the FET, with hormonal medications.
Fresh embryo transfer might not have been opted, for various reasons. For example, the couple cannot have FET if they the woman has caught a flu or is suffering from any other illness after egg retrieval but before transfer. If the endometrial conditions do not look good on the ultrasound, the fertility doctor may recommend cryopreserving all embryos, then scheduling FET-IVF for a later date.
Some couples choose to donate their unused embryos to another infertile couple. If a couple decide to use an embryo donor, their cycle will be a frozen embryo transfer.
Ovarian hyperstimulation syndrome (OHSS) is a risk where fertility drugs that can (in severe and rare cases) lead to loss of fertility and even death. If the risk of OHSS appears to be high before a fresh embryo transfer, it gets cancelled. When this happens, all the embryos are cryopreserved. Cancellation is necessary because pregnancy can exacerbate OHSS. It can also take longer to recover from OHSS if the womanis Once she recovers from OHSS, a frozen embryo transfer cycle is planned.
Studies have found that the success rate of pregnancy is better with frozen embryo transfers than with fresh embryo transfers. Studies have also found that pregnancies conceived after frozen embryo transfer has better outcomes. However, most studies have shown in younger women have a good prognosis. The prognosis for women over 35 years of age is unclear.
If opting for FET, the couple should consult a good fertility expert as they will be the best people to advise further treatment after looking into the medical history.
A frozen embryo transfer cycle has very little risk. One risk of using IVF (and fertility drugs) is ovarian hyperstimulation syndrome (OHSS). However, you don’t need to worry about OHSS in a FET cycle because ovarian stimulating drugs are not in use. Pregnancies from frozen embryo transfers might be healthier than those from fresh embryo transfers. Research has shown that frozen embryo transfer babies were at lower risk for premature birth, stillbirth, and low birth weight.
Embryo transfer has risks, including an increased risk of ectopic pregnancy and a risk of infection. Depending on the number of embryos transfer, the chance of multiple pregnancies may also be higher (which comes with its own set of risks for a pregnant person and the fetuses they are carrying).
Couple need to plan for a cost that includes investigations, consultations, ultrasound monitoring, hormonal support, and the costs associated with the transfer process. There is usually some amount of luteal phase support – medications that are given as ‘supplement’ for the successful continuation of conception. Cost of a FET cycle is usually much lesser than a full IVF cycle.