What is frozen embryo transfer (FET)?

Frozen embryo transfer is a part of the standard ART procedure where embryos, that are not fresh but preliminary thawed after cryopreservation (freezing), are tranferred into the uterine cavity.
The method of embryo cryopreservation appeared almost half a century ago. In 1983, there was a first pregnancy case after the use of cryopreserved embryos.
Recently, a method of "rapid" freezing of embryos has been developed, which is called vitrification. The essence of this method is that the embryo of the 5th-6th day of its development is placed in special devices (cryotope, carrier, straw) and then in liquid nitrogen at a temperature of -196º. Vitrified embryos can be stored in the cryobank for an unlimited amount of time. The storage period does not significantly affect the quality of the embryos and does not reduce the chances of implantation after the embryos are thawed.

Why do patients keep frozen embryos?

As a result of the ART cycle, we can get several good quality embryos at once. However, it is recommended to transfer one or a maximum of two embryos into the uterine cavity. This is due to a decrease in the possibility of multiple pregnancies (twins, triplets), which can lead to various complications during gestation.
For women with a reduced or low ovarian reserve in a natural cycle or a cycle with minimal hormonal stimulation, when we can expect to receive one or two embryos, the "embryo accumulation" program can be recommended. In this case, several (two or more) consecutive IVF cycles are carried out with the accumulation of embryos (their freezing) for subsequent transfers into the uterine cavity.

What is the difference between fresh and frozen embryo transfer?

Fresh transfer is the transfer of the embryo into the uterine cavity in the cycle when the stimulation of superovulation and puncture of the follicles was carried out.
Cryo transfer is the transfer of a thawed embryo into the uterine cavity after vitrification (rapid freezing). This method has practically no effect on the quality of embryos and does not reduce the chances of implantation after thawing.

When is frozen embryo transfer used?

  1. if more than two embryos of good quality are received in the IVF program, 1, 2 embryos are transferred into the uterine cavity.The rest are cryopreserved for planning subsequent pregnancies;
  2. in the absence of conditions for transfer in a "fresh" cycle:
    • the risk of developing ovarian hyperstimulation;
    • pathology of the endometrium;
    • the presence of acute inflammatory diseases of the mother by the day of transfer (acute respiratory viral infection, exacerbation of chronic disease);
    • conducting preimplantation genetic testing (PGT);
  3. Creation of a "personal" embryo bank.

Benefits of frozen embryo transfer

  1. Significantly reduces the risk of developing ovarian hyperstimulation syndrome.
  2. Allows conducting PGT (genetic testing of embryos).
  3. Makes it possible to correct the problems associated with the pathology of the endometrium before embryo transfer.
  4. Has higher efficiency than fresh transfer as statistics show.
  5. Preservation of embryos before planned treatment (oncology treatment).
  6. Delayed motherhood.

Frozen embryo transfer technique

There are two options for frozen embryo transfer, depending on the presence of female ovulation in the menstrual cycle.

  • Option 1: frozen embryo transfer in a fresh cycle (suitable for women with ovulatory cycles).

    The follicle growth is monitored and after confirmation of the fact of ovulation, progesterone medications are prescribed (to support the second phase of the menstrual cycle). Further, the transfer of pre-thawed embryos is carried out on the 5th day after ovulation.

  • Option 2: frozen embryo transfer using hormone replacement therapy (suitable for women with a hormonal factor of infertility).

    When choosing this option, a prolonged-acting GnRH is injected and after 14-16 days a pelvic ultrasound scan is performed (to monitor the thickness of the endometrium and confirm the absence of ovarian follicular cysts). Afterwards, estrogens are prescribed for 14 days with further ultrasound monitoring of the endometrium thickness. Finally, progesterone medications are prescribed for 7 days and frozen embryo transfer is performed.

Frozen embryo transfer success rates at Nadiya Odessa clinic of reproductive medicine

FET success rate is 43% per one attempt

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