By Bradford Kolb, MD, FACOG Board Certified, Reproductive Endocrinology and Infertility
Reproductive medicine has provided many wonderful options for women seeking to preserve their reproductive potential. From the advent of medications to stimulate egg production, to the development of in-vitro fertilization (IVF), many individuals have benefited from this technology. IVF is now commonplace and is no longer considered experimental or unusual. Fertility preservation (egg freezing) uses some of the same technologies perfected with IVF to allow women to delay childbearing. Egg freezing prevents the eggs from aging and therefore can be used to minimize the loss of fertility that occurs with advancing age. This loss of fertility starts in the late twenties and rapidly accelerates in the mid-thirties so that most women in their early forties have permanently lost their ability to conceive. The best option currently available to preserve fertility is to freeze eggs. By freezing one’s eggs, a woman is essentially preserving her egg’s potential for the future – eggs frozen from a 30-year-old women will
always function as if they came from a 30 year old, even if they are not used for another 10 to 15 years.
Egg freezing is the best option for the right patient. When an egg is frozen, its fertility potential is preserved indefinitely. Due to the natural loss of fertility that occurs with advancing age, we strongly recommend women freeze their eggs before their mid-thirties and most certainly before age forty. It is important that you have confidence in the center providing this service.
The Science Behind Egg Freezing
The major problem encountered in freezing tissue or individual cells is the damage that occurs when water in the cell forms ice crystals and damages the cell membrane (a protective barrier that allows the cell to survive). Small cells like sperm have been successfully cryopreserved (frozen) for many years. This is due to the small size of the cell and its low water content. With the advent of IVF we have learned to fertilize eggs (thus creating embryos) and to successfully freeze them so they could be used at a later date. Embryos are quite large, but when fertilized, the cell membranes change and become more tolerant of the freezing/thawing process. In addition, the use of agents called cryoprotectants have successfully minimized the adverse affects of ice crystal formation that can destroy the embryo. Cryoprotectants act as “antifreeze”, protecting the delicate egg against temperature changes. More recently, the ability to successfully freeze, thaw and fertilize eggs has
made egg freezing a realistic procedure to preserve a woman’s fertility. In addition to developing new freezing protocols and cryoprotectants, it is necessary to fertilize frozen/thawed eggs using a laboratory technique called ”Intracytoplasmic Sperm Injection” (ICSI) which involves the direct insertion of sperm into the egg. This manner of fertilization is necessary due to changes that occur in the cell membrane that would inhibit natural fertilization.
Egg Freezing Techniques: Competing Sciences
Over the last several years, two techniques have emerged to freeze eggs. The first technique, slow freezing, was the first to lead to significant improvements in freezing technology. This technique is similar to the process utilized by most fertility clinics to freeze embryos, so it is easily adapted for eggs. This traditional cryopreservation technique involves several steps that include a 15 to 20 minute incubation in low concentration cryoprotectant solutions followed by a one- to two-hour slow cooling process in a programmable freezer. Once the instrument reaches the desired temperature, generally <-35° Celcius, the vessel is removed from the programmable freezer and plunged directly into Liquid Nitrogen (-196° Celsius). One of the key objectives of slow cooling is to slowly remove the water from the cells so that no intracellular ice crystals form when the liquid goes through the phase change from a liquid to a solid.
The second technique utilized to cryopreserve embryos is a relatively new process called vitrification. This is very different than the slow freezing process resulting in the instant freezing of the egg. Data from this process are promising, but the technique is relatively new and evolving rapidly.
Vitrification is different in that the procedure relies on relatively high concentrations of cryoprotectants and is an ultra-rapid procedure. Once the egg has been placed in the cryoprotectant solution, the vessel with the egg is immediately plunged into the liquid nitrogen. The technique does not require the use of a programmable freezer. By definition, vitrification means solidification through increased viscosity, i.e. no phase change, hence less chance of intracellular ice crystal formation.
Limited data are available that accurately compare these techniques. Both techniques have resulted in comparable live birth outcomes. We continue to research both techniques to see which is the best procedure for our patients.
While data are limited, it appears that egg freezing is not associated with a statistically increased risk of birth defects, or physical or cognitive developmental problems in the offspring. Both techniques can be successfully utilized.
Who Should Consider Egg Freezing
The ability to preserve unfertilized eggs is profound and appeals to a variety of patien
- Single women in their thirties electing to delay childbearing. As professional and personal opportunities have advanced, many women have chosen to postpone child bearing. Women are born with a limited number of eggs and start to experience diminished fertility in their late twenties which rapidly accelerates in their thirties. Misunderstandings are abundant regarding fertility options for women. This is perpetuated with many high profile women who have successfully conceived (without revealing that they conceived using donor eggs). In addition, sociologic studies confirm that many women do not understand that fertility wanes with age and many women feel that delayed childbearing will not present a problem. Also, the medical community is only now beginning to educate women about the natural loss of fertility that occurs with advancing age. Fortunately, egg freezing is a proven method for delaying fertility. The following factors have not been shown to extend a women’s fertility: a late onset of puberty, the use of birth control pills, the
age that their mother conceived, one’s general health/diet/fitness or the simple belief that fertility will not be an issue. The decline and eventual loss of fertility is a simple and unfortunate biological fact. Egg freezing now allows women to suspend this loss and provides women more flexibility in regard to their reproductive options.
- Single women of any age undergoing treatment for cancer or other conditions resulting in the loss of their fertility. With the advent of improved diagnostic techniques and treatment options, many young women diagnosed with cancer are surviving and will go on to have families of their own later in life. Unfortunately, many of these life saving treatments will result in the loss of a woman’s fertility. Many chemotherapeutic agents have been shown to be detrimental to the ovaries. Exposure of the ovaries to radiation damages the eggs as well. The other factor that needs to be considered is that many oncologists will request that their patients do not conceive for at least two to five years after treatment so as to minimize the risk of reoccurrence during pregnancy. This delay in time only compounds the problems associated with the affects of chemotherapy on egg numbers and quality. Egg freezing before radiation or chemotherapy can preserve the eggs before they are damaged. It is critical that cancer patients explore egg freezing as soon as possible to see if this is an option. Since time is of the
essence, it is important that egg freezing is done as soon as possible before the initiation of treatment.
- Couples undergoing IVF with ethical concerns about embryo freezing or discarding embryos. Egg cryopreservation will allow for these couples to freeze excess eggs (as opposed to embryos) and maximize the benefit of their treatment. Couples can proceed with the creation of a limited number of fresh embryos for immediate treatment and then freeze the excess eggs. Frozen eggs can be utilized later if desired or simply discarded if not needed, thus avoiding the ethical dilemma of having extra embryos.
Why Choose HRC Fertility
There are many programs offering egg freezing as a treatment option. Many have not produced a single successful birth and are unable to utilize the variety of cryopreservation techniques that best fit the needs of the individual patient. HRC Fertility has spearheaded the creation of the largest research consortium in 2004 and its treatment protocols have been adopted by many centers. Currently our egg survival rate (percentage of eggs that remain viable after being cryopreserved and thawed) is in the 80 to 90% range and our pregnancy rate is comparable to our fresh embryo transfer rates. HRC Fertility is leading the nation to make egg freezing a financially feasible option for our patients and more widely available. Our goal is to allow women to be able to delay childbearing until they are ready to conceive in a manner that is affordable and highly efficient with the highest standards of medical science.