Egg Freezing or Oocyte Cryopreservation
Egg Freezing or Oocyte Cryopreservation. It is a procedure to preserve a woman’s reproductive cells or eggs by freezing and fertilizing them outside the woman’s body at a future opportune moment via assisted reproductive technology.
The steps of egg freezing or oocyte cryopreservation are:
- Ovarian stimulation begins with transvaginal ultrasound examination and blood tests to determine the number of oocytes and ovarian function and administering ovarian-stimulation medication for 9-12 days. The doses required vary among patients, depending on their ovarian functions. Follow-up ultrasounds will see whether the egg size and number meet the specifications. If it is, administering another medication will help the eggs mature.
- Egg retrieval is performed by transvaginal ultrasound-guided needle aspiration and suction to harvest the eggs from the follicles. It is a minor procedure performed under IV sedation given by an anesthesiologist. Patients must not eat or drink for at least 8 hours before the procedure. Egg retrieval takes around 30-45 minutes, depending on the number of retrievable oocytes.
- An embryologist selects healthy eggs for freezing. The temperature is precipitously cooled down to prevent ice crystal formation that can damage egg cells. When it is time for fertilization, an embryologist thaws the eggs and warms them to body temperature according to a laboratory protocol. The oocyte quality will be checked and assessed before fertilization with a sperm to produce a zygote that quickly begins dividing to become an embryo. At the blastocyst stage, it is transferred into the uterine cavity for subsequent implantation and pregnancy to take hold.
Current studies indicate that for women younger than 35 to have a successful pregnancy, at least 8-10 healthy frozen eggs are required.
Success depends on the quantity and quality of the eggs and their age when harvesting and freezing eggs. The younger the eggs are, the higher the success rate.
Advantages of egg freezing or oocyte cryopreservation
- Suitable for women who want to freeze their eggs for future in vitro fertilization when they are ready for pregnancy.
- Suitable for those who want to freeze their eggs before chemotherapy or radiotherapy, which can damage the ovaries.
- Suitable for those with genetic disorders causing premature ovarian failure, or those with ovarian dysfunction such as chocolate cyst
- To treat infertility with IVF. If the male partner has ejaculation problems or produces no sperm on the day of egg retrieval, freeze the eggs for future use.
- To freeze the eggs for donation.
Successful Fertilization Rates of Frozen Eggs
The success rate depends on the quantity and quality of the eggs and their ages. Usually, the survival rate of frozen-thawed oocytes is around 80-90%. The success rate of fertilization is 70-80%. After successful fertilization, the embryo will begin to grow for another five days, reaching the blastocyst stage, which is suitable for implantation. The success rate of development to the blastocyst stage is around 60%.