A frozen embryo transfer is commonly known as FET. In an IVF procedure, embryos are created and transferred into a woman’s uterus. There are generally 4-5 embryos created. One or two fresh quality embryos are transferred and rest viable embryos are thawed and freeze for future and can be used later. These embryos are preserved through cryopreservation. Couples prefer cryopreservation rather than going through multiple fresh IVF cycles as it is less expensive and time-consuming as well.

The whole procedure of IVF and frozen embryo transfer usually takes around six to eight weeks. Frozen embryo transfer itself takes around three weeks to complete.

Stages in FET

  • Pre-screening stage

Initially, all medical and fertility history is discussed. 

Doctors will also perform an ultrasound and adequate blood tests to diagnose for any genetic disorder, ovarian strength, etc.

  • Oral medication

Usually, birth control, estrogen injections, and other medications are prescribed three to four weeks of birth controls to regulate the hormonal cycle.

  • FET preparation

After an ultrasound, estrogen pills are given to prepare the endometrial lining. The rise in estrogen levels triggers ovulation and causes ovaries to start the production of progesterone. Progesterone then leads to the development of the endometrial lining.

  • Embryo transfer

 A fertilized egg needs to implant in the endometrial lining for the development of pregnancy. The right synchronization between progesterone and endometrial lining gives the required environment for healthy implantation. 

Need to freeze embryos 

  • During the process of the IVF cycle, we can create more than one embryo. In case, a fresh IVF transfer fails, a couple can use their cryopreserved embryos because only one or two are transferred at a time and rest as freezes for later requirements. It, even more, cost-effective to use cryopreserved embryos. Transferring multiple embryos at a time increases the risk of multiple pregnancies.
  • When a couple wants to have a sibling for their IVF conceived child, they can use their cryopreserved embryos as they can remain on ice indefinitely. A couple can also go for a fresh cycle of FET IVF but that is quite an expensive route.

There are couples with the risk of passing assured genetic conditions to their children. So to avoid those problems, the embryos are tested for such genetic mutations. This is termed as preimplantation genetic diagnosis (PGD). 

  • Preimplantation genetic screening (PGS ) is another kind of test that is done to look for any abnormalities in chromosome number, like trisomy21, that v=causes down syndrome is also performed. Once the egg is retrieved and fertilized, the embryologist will perform a biopsy for each appropriate embryo on its fifth or sixth day of development. the embryos whose test results come fine will only be allowed to transfer in the uterus of a woman and help the couple to overcome the problems of genetically passing disorders.
  • Sometimes, a fresh embryo transfer is canceled because of many reasons like flu, viral, or any other illness after the egg retrieval and before transfer. In those cases, rather than going for a fresh transfer, a cryopreserved embryo transfer is recommended. 

Process of storing embryos

Freezing technique i.e., vitrification is used extensively for freezing embryos. Vitrification is an egg freezing process which helps in storing them for later use. The technique used to freeze embryos is appropriately called slow freezing. In slow freezing, firstly embryos are placed in straws that are sealed from both ends. Now they are cooled down until the temperature of -30o Celsius. After which these straws are kept in tanks filled with liquid nitrogen at the temperature of -196ocelsius until the time of thawing. Embryos are then incubated in a chemical called cryoprotectants. These chemicals draw the water out of the embryo before the embryos freeze. Ice crystals are avoided in the cells by removing water out of them and replacing them with cryoprotectants.

Afterward, when slow frozen eggs are thawed, the cryoprotectants are again drawn out and water is released back into the cells. This process of thawing is performed very slowly and carefully in small steps to prevent an embryo from rupturing and dying during the process.

The slow freezing process of freezing embryos is capable of preserving a human embryo for around 30 years. This is one of the safest methods and can be successfully used for embryos at all stages of development. 

Risk in FET-IVF

  • The risk associated with frozen embryo transfer is much less than in the full IVF cycle. There is a risk of ovarian hyperstimulation syndrome (OHSS) in the case of IVF but there is the least risk of OHSS in frozen embryo transfer because ovarian stimulation drugs are not used.
  • The risk of multiple pregnancies (twins or triplets) also increases which depends on the number of embryos transferred. The twins or triplets pregnancy comes with an increased risk to mother and babies.
  • A study even said that in frozen embryo transfer there is a low risk of stillbirth, preterm birth, and even lower risk of low birth weight.

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Is the egg retrieval painful?

During egg retrieval, you will be sedated and given medication so that you don’t’ feel the pain. After the surgery/procedure, you may feel cramps, soreness, or fullness.

Is bleeding expected after egg retrieval?

After egg retrieval, vaginal bleeding/spotting is common. It is similar to bleeding in periods. In case of excess bleed, you should contact the doctor immediately.

How long do I have to stay in the hospital during and after the procedure?

IVF Procedure does not require any hospitalization. It only requires frequent visits from time to time.

How soon can I return to normal life after IVF?

Once the embryo transfer is done, you can resume your normal life. You may experience cramps because there might be a minor swelling in the ovaries. Stick to a mild routine and avoid exertion as it may affect your chances of getting pregnant.