Successful Human Egg Freezing and Fertility Preservation
The fertility clinic where I work has established a successful Fertility Preservation (FP) program using a technique known as oocyte cryopreservation (egg freezing). This program is under my direction and that of Dr. Jamie Grifo. We are both full-time faculty at the NYU School of Medicine in the Department of Obstetrics and Gynecology.
Prior to 2004, only a handful of births from thawed, frozen eggs had been reported, but over the last 7 years, the technique has flourished. Today, more than 1,500 healthy babies have been born from oocyte freezing and thawing around the world. Importantly, the incidence of birth defects in these babies does not appear to be increased as compared to natural conceptions (Noyes et al, 2009). Still, the egg freezing techniques are exquisitely precise and have not yet been mastered by all in vitro fertilization (IVF) programs. Our clinic has been able to achieve a pregnancy rate with egg freezing similar to that of conventional IVF cycles. To date, at least 50% of the women who have had their eggs frozen before age 40 and subsequently thawed have delivered a baby or are currently carrying an ongoing pregnancy. Egg freezing is particularly useful for women of reproductive age diagnosed with a malignancy requiring chemotherapy or surgery that will render them infertile. It can also be used to extend childbearing potential for a variety of other reasons.
Egg quality is best when a woman is in her reproductive prime, meaning between the ages of 16 and 28. A women's eggs are usually still of good quality in the mid-reproductive years (meaning between the ages 29 and 38) and may remain usable (but definitely with diminished chance for producing pregnancy) in the late-reproductive period (age 39 to 44 years). If necessary or possible, it is ideal to have eggs that are frozen when they are of the best quality possible. For instance, eggs frozen at the age of 35 are superior to fresh eggs produced at 43 years of age. In addition, eggs frozen prior to chemo- or radiation therapy that is known to affect ovarian function is preferable to freezing after these treatments have been started.
An oocyte cryopreservation treatment cycles starts the same way as a regular IVF treatment cycle and involves stimulating the woman's ovaries with a fertility medication called follicle stimulating hormone (FSH). Normally, during the reproductive years, a woman's body releases one egg from the ovary near the middle of each menstrual cycle. The fertility medication stimulates maturation of more than the usual one egg so that multiple oocytes can be obtained from one treatment cycle. Follicle stimulating hormone is administered as a daily subcutaneous injection for about one week, during which time monitoring of the ovarian response is necessary (through blood tests and sonograms). Once the eggs are deemed ready by the doctor, a late-night shot is necessary, followed 1-1/2 days later by the oocyte harvest procedure, commonly known as the "egg retrieval". The harvest is performed under mild sedation and takes about 10 minutes to complete. Once removed from the body, the eggs are brought to the clinical laboratory where they are initially evaluated for health, and then frozen. The number of oocytes retrieved varies from woman to woman and may be anywhere from 0 to 45, depending on a woman's age and how the individual woman's body responds to the fertility medications.
The average number of eggs retrieved from women freezing for the purpose of deferring reproduction at the NYU Fertility Center is currently 15, the range being 2 to 55. To date, medical egg freeze cycles (e.g. those performed for cancer patients) have resulted in an average of 20 eggs retrieved (range 1 - 61) with 14 mature eggs frozen. Our center currently has an ongoing pregnancy in a breast cancer patient who froze oocytes at age 40.5 and thawed them at age 43. The represents the oldest cancer survivor worldwide to be pregnant from frozen-thawed oocytes. Having said that, it's important to appreciate that not all oocytes are suitable for freezing. Usually only about three-quarters of eggs are mature and only mature eggs are currently frozen for later use. It is important to point out that not all eggs are meant to be babies and not even the healthiest appearing eggs can be guaranteed to create pregnancy.
At present, oocyte cryopreservation still has an experimental designation, but the technology is considered promising by the American Society of Reproductive Medicine. This is in part due to the fact that many centers around the country currently offering egg freezing have never had or have a very low success rate regarding pregnancy. In addition, there have been many fewer babies born from egg freezing and thawing than from embryo freezing and thawing, or from regular fresh IVF treatment cycles. At NYU, we have worked hard to establish a successful oocyte cryopreservation program and are pleased that we can offer this treatment option to women at this time.
