Embryo Freezing

What Is Embryo Freezing?

In case of a frozen embryo transfer (FET), previously frozen embryos from a new IVF round are thawed and placed in a woman’s uterus. By doing this, the necessity for an additional round of hormone stimulation and egg harvest is avoided.

Why Is It Done?

  • If a couple is not ready for pregnancy right away but wants to try later, embryo freezing may be a possibility.
  • Because of high numbers of follicles developing, hormone production can occasionally increase dramatically during ovarian stimulation. Embryos are frozen in this situation to prevent the emergence of complications such as ovarian hyperstimulation syndrome (OHSS).
  • If during the IVF cycle, a large number of embryos are created, usually one or two embryos are transferred, and the remaining embryos are frozen to avoid achieving multiple pregnancies and associated risks.
  • Genetic disorders: If either couple is having some genetic disease, that their offspring might potentially inherit, is recommended to have a pre-implantation genetic screening. Here some cells are biopsied from the embryo, and genetic analysis is conducted. Healthy embryos which are devoid of any disease are then transferred.
  • Fertility preservation: If a woman is undergoing cancer treatments such as radiation or chemotherapy that could harm her fertility, freezing embryos is an option. These can be transferred later after cancer treatment.

What Can You Expect?

  • To increase the number of eggs produced by the ovaries—rather than just the one that typically develops each month—hormonal medications (injection FSH/HMG) are administered. It is necessary to use multiple eggs because some eggs won’t fertilise or develop normally following fertilisation.
  • The growth of the follicles in which eggs mature is observed using vaginal ultrasonography of the ovaries. Blood tests are also performed to assess the effectiveness of ovarian stimulation drugs; progesterone levels are normally low until after ovulation, while oestrogen levels typically rise as follicles form.
  • Medicines to stop the body from releasing the developing eggs too early.
  • Human chorionic gonadotropin (HCG) or other medications are administered to help the eggs mature when the follicles are prepared for egg retrieval. This is usually done after eight to 14 days.
  • If a woman is undergoing cancer treatments such as radiation or chemotherapy that could harm her fertility, freezing embryos is an option. These can be transferred later after cancer treatment.
Egg Collection

After the last injection and before ovulation, egg retrieval is typically scheduled 34 to 36 hours later. Sedation is used during this treatment to make it painless.

  • The typical technique for retrieval is transvaginal ultrasound guided aspiration. To extract the eggs, a small needle is put into an ultrasound guide to pass into the vagina and the follicles.
  • A needle attached to a suction tool is used to retrieve the eggs from the follicles. In around 20 minutes, several eggs can be taken out. The more eggs that are extracted, the higher the likelihood of becoming pregnant.
  • The patient may suffer cramps, a sense of fullness or pressure, and other post-egg retrieval symptoms.
  • The culture medium (which contains nutrients) is used to incubate mature eggs. Aiming to produce embryos, sperm and eggs that seem healthy and mature are combined.

Sperm Extraction

If a partner’s sperm is used, he will provide a sperm sample via masturbation on the morning of egg retrieval. Other methods, such as testicular aspiration (the use of a needle or surgical procedure to extract sperm directly from the testicle), or donor sperm, are sometimes required.


Fertilization can be accomplished in two ways:

Conventional insemination: This procedure involves combining healthy sperm and mature eggs in a culture medium, where the sperm fertilizes the egg through natural motility.

Intracytoplasmic sperm injection (ICSI): ICSI involves injecting a single healthy sperm directly into each mature egg. ICSI is often used when sperm quality or quantity is an issue or if previous fertilization attempts during IVF cycles have failed.

Embryo Freezing:

The most common method for freezing embryos is known as vitrification. The water inside the cell is replaced with cryoprotectant substances during this process. It is then followed by rapid cooling, which prevents ice crystals from forming inside the cells and thus increases embryo survival during the thawing process. Embryos are then placed in plastic straws with the patient’s name and identification number written on them. Embryos can be frozen for many years in tanks filled with liquid nitrogen using this method.

Frozen Embryo transfer

Transplanting a frozen embryo:

  • Uterine lining preparation: The development of the uterine lining is aided by the administration of hormone-based drugs. To make the lining receptive to the embryo, progesterone supplementation is administered. The process for transferring the embryo is scheduled when it is determined that the lining is of a favourable thickness and has healthy blood flow.
  • Thawing: The embryos that will be transferred are gradually brought to room temperature during the thawing procedure by being taken from the storage tank.
  • Although the patient may feel some light cramping, embryo transfers are often painless procedures. The cervix and uterus are reached through the vagina by inserting a long, thin, flexible tube known as a catheter. The catheter has an attachment at the end that holds a syringe with one or more embryos suspended in a little volume of fluid. Afterward, the uterus is forced to receive the syringe’s contents.
  • Embryos to be transferred in number: The quantity of embryos to be transplanted is normally determined by the age and quantity of recovered eggs. Most often, more embryos are transplanted since older women have a lower rate of implantation. Extra embryos may be frozen and kept for a few years in case they are needed in the future.
Results :
  • The patient can get back to his or her regular daily routine following the embryo transfer.
  • When opposed to fresh embryo transfer, which carries the risk of OHSS, frozen embryo transfer carries much lower hazards.
  • A blood test (beta-hCG) is performed to determine whether the patient is pregnant 12 days to 2 weeks following embryo transfer.
  • The doctor will begin or refer the patient for prenatal treatment if her b-HCG test results indicate she is pregnant.
  • A woman is advised to discontinue taking progesterone if she tests b-HCG negative, meaning she is not pregnant. She will likely start menstruating within a week. She will be advised to undergo a frozen embryo transfer in the subsequent cycles if she still has any frozen embryos.

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