Egg freezing

In women, fertility declines with age. Those in their twenties and thirties have lower rates of miscarriage and fewer babies with birth defects. This is largely due to the increase in the percentage of embryos with chromosome abnormalities that occurs with age. Because of the problems associated with reproductive aging, many have chosen to use donor eggs to increase their chances of having a child. While this method has proven to be very effective, it is often a hard choice as it entails the greatest sacrifice. With advances in cryopreservation, freezing eggs at a younger and more fertile age has the potential to allow individuals to be their own egg donors later in life.

Normally, when performing in vitro fertilization, the eggs are matured inside the body using fertility drugs. The eggs are removed after they are thought to be mature, which is necessary for it to be fertilized with sperm. These mature eggs can also be frozen.

If there is urgency to begin cancer treatment or if cancer makes ovarian stimulation risky, eggs can be retrieved while still immature. It may then be possible to mature the eggs later on after thawing. This technique, known as in vitro maturation, or IVM, involves maturing eggs outside of the body in a laboratory setting. This procedure does not require hormonal fertility medications, and thus may be a better choice for women who want or need to avoid stimulation with fertility drugs.

In October 2012, the American Society for Reproductive Medicine (ASRM) concluded that there is now ample data to support that fertilization rates and pregnancy rates are similar to IVF when using fresh or frozen eggs in young infertility patients and egg donors. In addition, there has been no noted increase in chromosome abnormalities, birth defects, or developmental defects in children born from frozen eggs. Therefore, the freezing of eggs should no longer be considered experimental.

Data has shown that egg freezing has shown gradual improvement over time with better survival, better pregnancy rates, and lower miscarriage rates. Recent slow freeze studies have reported a miscarriage rate that is comparable to the rate seen in naturally conceived pregnancies. Live birth rates upon thawing, fertilization, and transfer of cryopreserved eggs by either the slow freeze method or by vitrification compare favorably to the rates seen with frozen embryos in many programs. However, in programs that have very high frozen embryo pregnancy rates (such as at IVF1), egg freezing is still not as successful as embryo freezing.

As noted above, eggs thawed after rapid freezing that successfully become blastocysts seem to have an equal chance of producing an ongoing pregnancy. A recent study from Canada showed that the rate of birth defects was 2.5% in babies conceived after freezing of eggs. This is comparable to the rate seen in babies conceived naturally and from IVF. Other reports have found that the incidence of chromosome abnormalities in human embryos derived from frozen eggs is no different than the rate seen in fresh embryos. A study of 200 babies born from vitrified eggs also failed to find any difference in birth weight.  

While embryo cryopreservation is still the method of choice for most couples, it has many limitations for those without partners. An individual may face discomfort with choosing a sperm donor, paternity and legal obligations in the case of a known sperm donor, and the disposition of frozen embryos if marriage occurs in the future. With frozen eggs, in the case of divorce, separation, or abandonment, disposition may be easier to handle. In the end, if pregnancy rates after egg cryopreservation continue to increase, the rate of multiple pregnancies could decrease with the use of more conservative practices such as fertilizing fewer eggs and transferring fewer embryos.

Slow Freezing: This method involves introducing a low concentration of cryoprotectant to eggs at a warm temperature, gradually lowering the temperature to -6°C, and then rapidly cooling them in liquid nitrogen to prevent ice crystal formation. Thawing is done quickly to avoid damage from ice crystals.

Rapid Egg Freezing (Vitrification): Vitrification, a rapid egg freezing method with high cryoprotectant concentration, significantly improves egg survival and pregnancy rates. It is suitable for those undergoing fertility-threatening treatments or those without a current partner who want to preserve their fertility for future family planning.

Ovarian Tissue Freezing: An alternative to egg freezing, ovarian tissue freezing involves freezing strips or entire ovaries, preserving the ovarian cortex where most eggs are located, commonly used for cancer patients. It allows for later transplantation, with ovulation typically returning in three to four months, but grafts have a lifespan of about three years or less.