Egg freezing or oocyte cryopreservation refers to the freezing of eggs (oocytes) to sub-zero temperatures to stop its biologic activity, keep it in a frozen state, and preserve them for future use. When the eggs are thawed at a future point in time, they resume normal function and can be fertilized.

A woman’s fertility naturally diminishes over time as the quantity and quality of the eggs decreases. Before 2012, egg freezing was still considered an experimental procedure for preserving fertility and not widely available. Only embryo freezing was available to the public for those interested in preserving fertility. Today, egg freezing is quickly becoming a sought after procedure for those interested in preserving their fertility for personal reasons. Egg freezing enables the preservation of the woman’s fertility by freezing her eggs before the quantity and quality of the eggs become low.

 

Who should consider egg freezing?

The demand for egg freezing is rapidly expanding. It is commonly used in egg donations and in women with cancer to preserve their fertility as cancer therapy often causes infertility.

The American Society for Reproductive Medicine (ASRM) lists the following cases when egg freezing is indicated:

• Immediate threat to fertility because of chemotherapy or pelvic radiation therapy
• Surgery associated with risk of damage to the ovaries
• Ovarian disease (e.g., endometriosis) with risk of damage to the ovaries
• Risk of premature ovarian senescence because of Turner’s syndrome (45,XO), the fragile X syndrome, or a family history of premature ovarian failure
• Genetic mutation requiring oophorectomy (surgical removal of ovaries)
• Failure to obtain sperm by means of testicular sperm extraction on the day of oocyte retrieval
• Excess oocytes during in vitro fertilization along with ethical objection to or program specific restrictions on fertilizing more oocytes than will be transferred during one cycle
• Preservation of donor oocytes
• Preservation of fertility to delay pregnancy for personal reasons.

Recently, the use of egg freezing to preserve fertility in healthy women due to career advancement and life planning reasons have been rapidly increasing.

The public attention for egg freezing first hit headlines when Facebook and Apple announced that they would provide insurance coverage for the cost of egg freezing as an employee benefit. Egg freezing can provide women with more flexibility to pursue educational or career goals first while preserving their fertility for a later time.

To read more on the best time to do egg freezing, read here.

 

How is it done?

Egg freezing begins with the stimulation of the ovaries to produce mature eggs. The ovaries are stimulated once menses begins with injections of reproductive hormones for up to 2 weeks. The fertility doctor monitors the maturation of the eggs during this time using ultrasound to determine when the eggs are ready to be collected.

Once the fertility doctor determines the eggs are ready for collection, hCG (reproductive hormone) is administered to stimulate the final maturation process. About 34 to 36 hours after hCG is given, the woman undergoes a minor surgical procedure while being mildly sedated to collect the matured eggs. The collected mature eggs are then processed, frozen (typically by vitrification), and stored in liquid nitrogen at -196 degrees Celcius.

 

How many eggs do you need to freeze?

There is no exact number of eggs a woman should freeze in a cycle. The number of eggs collected will depend on the age of the woman, health status, ovarian reserve, and the protocol used at the IVF center. Typically 10-15 eggs are collected per cycle and these can be split into batches of 5 or 6 eggs to be used for more than one cycle. You can read more on the optimal number of eggs to retreive for IVF here.

 

How long can the eggs remain frozen?

There is limited data regarding the effect of storage time on egg viability and rate of live birth. One study in 2009 by Parmegiani et al. found there was no difference in the live-birth rates between fresh eggs and frozen eggs frozen for 48 months. The longest storage time for frozen eggs that resulted in a live birth was 14 years and 6 months.

 

Are pregnancy rates for using frozen eggs different from fresh eggs?

Many studies have demonstrated the use of frozen eggs have similar pregnancy rates to that of fresh eggs. The use of frozen eggs in IVF has been in practice for many years and is a standard part of IVF therapy. In one large trial by Cabo et al. in 2010, found no significant differences in the pregnancy rates per transfer between vitrified frozen and fresh eggs (55.4% vs. 55.6%.)

 

Are there risks to the baby born from frozen eggs?

The short-term data on children born from frozen eggs show no increased risk of congenital anomalies when compared to the general population. However, there is limited long-term data on children born from frozen eggs. Currently, the available data show no increased safety issues in children born from forzen eggs compared to children born conventionally.

 

 

 

Reference

Glenn LS. Cryopreservation of Oocytes. N Engl J Med 2015; 373:1755-1760

Parmegiani L, Garello C, Granella F, Guidetti D, Bernardi S, Cognigni GE, et al. Long-term cryostorage does not adversely affect the outcome of oocyte thawing cycles. Reprod Biomed Online. 2009;19:374–9.

Urquiza MF, Carretero I, Cano Carabajal PR, et al. Successful live birth from oocyte after more than 14 years of cryopreservation. J Assist Reprod Genet. 2014;31(11): 1553.

Mature oocyte cryopreservation: a guideline. Practice Committees of American Society for Reproductive Medicine, Society for Assisted Reproductive Technology. Fertil Steril. 2013;99(1):37–43.

Cobo A, Meseguer M, Remohi J, Pellicer A. Use of cryo-banked oocytes in an ovum donation programme: a prospective, randomized, controlled, clinical trial. Hum Reprod. 2010;25:2239–46.

Noyes N, Porcu E, Borini A. Over 900 oocyte cryopreservation babies born with no apparent increase in congenital anomalies. Reprod Biomed Online. 2009;18:769–76.