What Is Frozen Embryo Transfer (FET)


Frozen Embryo Transfer Procedure & Treatment in Delhi

Frozen Embryo Transfer is a procedure designed to cryopreserve (freeze) surplus embryos or cryopreserve embryos in the fresh stimulation cycle to increase the overall success rate in couples undergoing the IVF process.

Indications of FET

  • Surplus embryos
  • Hormonal imbalance
  • Fluid in endometrium
  • Patient not medically fit for transfer
  • Couples who want to postpone pregnancy
  • Women who are embarking on cancer treatment
  • OHSS

What is the Process of Freezing Embryos

In slow freezing, the gametes are frozen at a slow temperature fluctuation of 0.3 to 2 degree celsius per minute until it reaches the final temperature of -196 degrees.

The exchange of intra and extracellular spaces, and low concentration of the cryoprotectants ensures safe freezing without serious osmotic and deformation affect to the cells.

Vitrification is called fast freezing or flash freezing in which non-equilibrium freezing is done with high concentration of the cryoprotectants, thereby completely eliminating the ice crystal formation. It doesn’t take too much time and is a quick process.

How Long Can Embryos Stay Frozen?

As per the Human Fertilisation and Embryology Act , the embryos or gametes can be frozen upto 10 years. In India, we can freeze embryos upto 5 years at a stretch after which we have to renew the freezing if needed.

Fresh Vs Frozen

In many cases FET leads to higher pregnancy rates especially in the indications cases such as hormonal imbalances, fluid in endometrium or thin endometrium. However, in other situations, especially in women with regular cycles, fresh embryos are transferred.

Thawing of embryos

Initially, the embryos are removed from liquid nitrogen to room temperature. At this stage the embryo is completely dehydrated by moving it into samples of low osmolality. It then regains its original shape and is placed in a culture medium for its continued growth.

Process of FET

The endometrium is usually prepared from the first or second day of the menstrual cycle through the administration of estradiol valerate. When the endometrial thickness reaches 8mm , progesterones are started and the embryos are transferred a few days later. Following the transfer, some medications are prescribed ( luteal phase support) for 2 weeks until the pregnancy test is done.

Success of FET

The success rate of FET depends on multiple factors like age of the patient, quality of eggs, sperms, embryos, endometrium, thawing and transfer technique.

Some information on the embryo cycle

Here’s a detailed overview of the embryo cycle:


The embryo cycle begins with the fusion of a sperm and an egg, leading to fertilisation. This usually occurs in the fallopian tube, resulting in a zygote.


The zygote begins to divide through a process called cleavage, forming a multicellular structure. These early-stage divisions lead to the formation of a morula and then a blastocyst.

Blastocyst Formation:

The blastocyst is a crucial stage in the embryo cycle. It consists of an inner cell mass that will develop into the fetus and an outer layer of cells that will become the placenta. The blastocyst must reach a certain stage of development to be considered viable for implantation.


The next phase is the implantation of the blastocyst into the uterine lining. This is a delicate process where the embryo adheres to the uterine wall, allowing for further development.


Organogenesis is the formation of organs and body structures within the embryo. This is a critical stage where the heart, brain, limbs, and other vital structures begin to take shape.

Fetal Development:

As the embryo develops further, it transitions into a fetus. This phase involves continuous growth and maturation of all body systems until the baby is ready for birth.

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Frozen Embryo Transfer (FET) is a procedure where cryopreserved embryos from a previous in vitro fertilization (IVF) cycle are thawed and transferred to the uterus during a carefully timed cycle. The uterine environment can be more controlled and receptive as a result, improving the likelihood of a successful implantation and pregnancy.

The process of freezing embryos involves cryopreservation. Viable embryos obtained through IVF fertilization are carefully frozen using cutting-edge methods.  The ability to store these frozen embryos for later use allows for timing flexibility when it comes to embryo transfer.

Frozen Embryo Transfer (FET) offers advantages over fresh embryo transfer by allowing for better synchronization between embryo readiness and the optimal uterine environment. Because frozen embryos can be stored and used in later cycles if necessary, it also offers planning flexibility.

Yes, patients at Advance Fertility can have greater control over the timing of Frozen Embryo Transfer (FET). This adaptability increases the chance of a successful implantation and a safe pregnancy by enabling strategic planning and ideal circumstances.

At Advance Fertility, hormones are used to create the perfect uterine environment in preparation for frozen embryo transfer (FET). For the purpose of synchronizing the endometrial lining with embryo implantation, hormonal treatments like progesterone and estrogen are carefully given. 

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