Treatment

Oocyte Cryopreservation

For many decades, cryopreservation of sperm and embryos has been performed successfully using the slow freezing method. However, when applied to eggs, the slow cooling technology has been disappointing due to the challenges of ice crystal formation that can damage the chromosomal plate during thawing. Although the first live birth from frozen eggs occurred in 1986, until recently, egg survival rates of 20% and pregnancy rates of <10% were too low to make egg cryopreservation practical.

In 2008, a new freezing technology called vitrification was introduced to freeze embryos. By taking cells from room temperature to -196 degrees C in a fraction of a second, vitrification completely avoids formation of ice crystals. The results are higher rates of embryo survival and live births. With some modifications, the vitrification process for embryos can be adapted to allow successful freezing of oocytes (eggs). Preliminary studies have shown that the ultra rapid freezing process completely avoids formation of ice crystals to allow achievement of egg survival rate of 80-90% and pregnancy rates of 50% or higher in certain groups of patients.

Egg cryopreservation can be beneficial for women who are about to undergo cancer treatment that can potentially compromise the ovaries. Certain types of chemotherapy or radiation therapies focusing on the pelvis can result in loss of eggs, sometime years after treatment. In addition, the surviving eggs may have irreversible damage to their genetic materials that can lower the chance of successful conception in the future.

More commonly, egg freezing will allow patients to avoid the ethical dilemma of discarding extra embryos. Instead of fertilizing all available eggs in an IVF cycle, some eggs can be frozen for future use. If the first treatment attempt is unsuccessful, the frozen eggs can thawed and fertilized via sperm injection (ICSI) to give the patient another chance to conceive.

Women who desire to bank their eggs for future use can also benefit from this new technology. Many women desire to postpone childbearing for a variety of reasons. Unfortunately, egg quantity and quality decline exponentially after the age of 35 and by age 40, the chance of a live birth will be quite low. By freezing her eggs when she is younger, a woman can preserve her reproductive potential at the time of freezing.

How safe is egg cryopreservation? Since 1986 there have been more than 2,000 live births from frozen eggs worldwide. Studies have shown only 1.3% birth abnormalities, which is not significantly different from that seen in naturally conceived infants.

It is important to remember that oocyte vitrification is still considered an experimental technology by the American Society of Reproductive Medicine. We are currently conducting a clinical trial on egg cryopreservation for patients of age 40 or below who desire to defer pregnancy due to personal circumstances.

back to top