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OOCYTE CRYOPRESERVATION: All You Need To Know.

OOCYTE CRYOPRESERVATION: All You Need To Know.

TSK_7685-min

Egg freezing or oocyte cryopreservation is the process in which a woman’s eggs (oocytes) are extracted, frozen, and stored as a method to preserve reproductive potential in women of reproductive age. 

The first human birth from a frozen oocyte was done in 1986. Oocyte cryopreservation has evolved greatly in the last few years as eggs survive the freezing process improved overall success. Thus, the American Society for Reproductive Medicine no longer refers to it as an experimental process. The technique leading to enhanced gamete survival, potential fertilization, and live birth rates now offer women the autonomy that wasn’t possible some years ago. 

Who Needs Egg (oocyte) Freezing?

Cryopreservation of the oocytes can be considered for a variety of reasons:

  • Women with cancer require chemotherapy and/or pelvic radiation therapy that may affect fertility.
  • Surgical procedures may cause damage to the ovaries.
  • Women who are at risk of premature ovarian failure because of chromosomal abnormalities (e.g. Turner syndrome, fragile X syndrome), or have a family history of early menopause.
  • Women with certain ovarian diseases that have a risk of damage to the ovaries.
  • Genetic mutations require removing the ovaries (e.g. BRCA mutation).
  • Fertility preservation for social or personal reasons to delay childbearing.

     

How is Egg Freezing Done?

Egg Freezing Process

First, your fertility specialist may perform an assessment of the ovarian reserve to estimate the potential yield of oocytes prior to the ovarian stimulation cycle. The assessment would include blood tests and pelvic ultrasound. This will also help to determine the necessary dose of medications. 

Ovarian stimulation is carried out in the same manner that is used with in-vitro fertilization (IVF), using injectable hormonal medications. Following the stimulation, the oocytes and the surrounding fluid in the ovarian follicles are aspirated vaginally while under sedation.

The maturity of the eggs is assessed under the microscope, and those that are mature are cryopreserved. Currently, vitrification is the method of choice for cryopreserving oocytes, and this is achieved by ultra-rapid cooling into liquid nitrogen where they can be stored.

How Will Eggs be Used in the Future?

When the woman is ready to use the frozen eggs to achieve pregnancy, these cryopreserved eggs are transferred to a warming solution and assessed. The eggs that survived the freezing process are fertilized through a process called the intracytoplasmic sperm injection (ICSI), during this procedure a single sperm is injected directly into the egg, and the fertilized eggs will then grow in culture until the embryo(s) are ready to be transferred into the uterus to achieve pregnancy, ideally, this takes places 3-5 days after fertilization.

Egg Freezing Success Rates

Clinical pregnancy rates have been estimated between 4-12% per oocyte. But since egg freezing is relatively new, more data will be needed to have a better idea of these success rates. In general, the two most important factors in determining the probability of live birth are the woman’s age at the time of egg freezing and the number of available eggs.

Factors that impact the success of egg freezing and thawing procedures include:

  • Age on freezing the eggs: Younger women tend to produce more eggs that are less likely to have anomalies.
  • Age at time of egg thawing and IVF: Younger women are more likely to have successful pregnancies.
  • Sperm quality: Healthy sperm is more likely to produce a healthy embryo and a successful pregnancy.
  • The clinic: The success rates of freezing and thawing eggs vary between clinics.
  • The number of eggs: Freezing a larger number of eggs offers more opportunities for successful IVF cycles.

How long will frozen eggs last?

Freezing an egg stops it from ageing. Most studies on frozen eggs examined eggs that were a few months in storage. The length of time for which a specialist can freeze eggs remains unclear.

What are the Chances of a Successful Pregnancy Using Frozen-thawed Oocytes?

Most researchers suggest freezing eggs in the mid-to-late twenties for use after 30 years of age. Women who are considering IVF in the future should not delay any longer than necessary. According to the University of Southern California’s fertility clinic, about 75 percent of eggs survive the thawing process.

Embryos are more likely to survive both freezing and thawing than eggs and are more likely to result in a successful pregnancy. Women with a partner or who intend to use donor sperm should consider freezing embryos rather than just eggs.

Are There Effects on the Offspring Conceived from Frozen-thawed Oocytes?

Available data comparing births resulting from previously frozen oocytes with those from fresh oocytes have not shown an increased risk of congenital anomalies. More long-term data, however, will be needed to further assess these risks.

What are the Risks Associated with the Oocyte Cryopreservation Procedure?

Risks are similar to those associated with ovarian stimulation for IVF, which include small risks of ovarian hyperstimulation syndrome (enlargement of the ovaries and fluid accumulation in the pelvis and abdomen), infection, and bleeding related to the egg retrieval procedure.

How Long Can the Eggs be Stored?

Storing the eggs for longer durations does not appear to have negative effects. However, data are only available for up to 4 years of storage. It must be remembered that older maternal age when carrying a pregnancy is associated with higher risks of pregnancy complications, such as high blood pressure, diabetes, and caesarean section. Most clinics have an upper age limit on when these gametes can be used to achieve pregnancy.

What to expect?

As a woman grows older, the quality of her eggs tends to decline. The eggs may contain more chromosomal abnormalities, and women will no longer ovulate after menopause. This means that her ovaries will cease to release eggs.

If a woman wants a child but is not able or ready to conceive at the present time, a dedicated facility can freeze her eggs for use at a later date

Are there side effects?

After egg retrieval, some women may experience cramping, bloating, weight gain, mood swings, headaches, and spotting. In rare cases, egg stimulation can lead to a condition known as ovarian hyperstimulation syndrome (HSS). 

The effects of HSS can include pain, nausea, and significant weight gain of over 10 pounds (lb) in 3–5 days. Very rarely, HSS might trigger blood clots in the legs and shortness of breath. 

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