21st Century IVF Centre, the first fertility/reproductive science center in Massachusetts to assist in a frozen egg pregnancy, is excited to offer an exciting new technology ~ egg freezing ~ to our patients. The purpose of egg freezing is simple ~ fertility preservation.
What are Some Reasons a Woman May Consider Freezing Her Eggs?
The most common reason to consider egg freezing is to stop the “biological clock”. For the first time in history a woman can prevent aging from affecting her fertility. The reason we can do this is that eggs are removed from the ovaries ~ then frozen ~ and do not age. Another reason to freeze eggs is to preserve fertility in woman about to undergo chemotherapy and/or radiation.
Age is the most important factor that affects a woman’s fertility. A woman’s fertility remains stable up to age 35-36 and then begins to decrease thereafter. The decline accelerates after the age of 40.
What is the Explanation for the Decline in Fertility with Age?
Simply put ~ it all has to do with the egg. As every woman gets older there is a decline not only in the number but the quality of eggs that remain in the ovaries. So, as every woman gets older there is a greater chance of infertility as well as a miscarriage. For those women betwen the ages of 40-44 years old, the incidence of infertility is 30-40% and for those that do conceive, the miscarriage rate is approximately 50%. After the age of 45, successful, spontaneous pregnancies are rare.Ideally, a woman who is not ready or in a position to start a family by the mid-to-late thirties should consider egg freezing to preserve her fertility.
How Do We Know That Fertility in Women Resides in the Egg?
We know this from experience with ‘egg donation’. For example, if a fertilized egg from a 25-year-old woman is placed in the uterus of a 45-year-old, the 45-year old woman has the fertility of a 25-year-old! Another issueto consideris that if a woman develops infertility later in life, success rates with treatments using her (older) eggss may be low. The graph below illustrates in vitro fertilization (IVF) success rates in the different age groups. So a woman undergoing IVF at age 42 has a 10% chance of successful pregnancy. But if that same 42-year-old woman used eggs that she had frozen at age 35, the success rate per cycle would be 35%. Depending on the number of eggs that are frozen, multiple IVF cycles may be attempted.
The History of Freezing
The process of freezing os not new to reproductive medicine. Sperm may be frozen for over 50 years and embryos (fertilized eggs) for almost 30 years. In the past the slow freezing technique was used. With this methode the tissue being frozen is exposed to cryoprotectants which are solutions that displace water from the cells and reduce the damage from the freezing and thawing process. Then over 1-2 hours the temperature is decreased to that of liquid nitrogen. The survival rate of sperm and embryos after thawing, following the slow freeze method, has been very good. While this process was adequate for sperm and embryos, eggs seem to be sensitive to this method of freezing. Over the past several years a new freezing method has been developed, called vitrification. The vitrification process involves exposing the eggs to a higher concentration of the cryoprotectants and then very rapidly freezing the eggs over just minutes. When this technique is to freeze eggs, the survival rate after thawing is 90%.
Candidates for Egg Freezing
The best candidate for egg freezing is a woman under the age of 40 and one who has adequate ovarian reserve of eggs. One way of assessing ovarian reserve is to take a blood sample and measure the levels of follicle stimulating hormone (FSH) and anti-mullerian hormone (AMH). In addition, a vaginal ultrasound can be performed to count the number of follicles in the ovaries (a follicle is the fluid-filled cyst that houses the egg). While this testing provides some insight into the ovarian reserve, the true test of ovarian reserve is a stimulated cycle where the woman takes injections of FSH.
The Egg Freezing Cycle
To start the egg freezing cycle, daily follicle stimulating hormone (FSH) injections are begun soon after the menstrual period starts. FSH is a natural hormone that stimulates the follicles to develop within the ovaries. The daily injections are self-administered with a small needle for a period of 7-10 days and during this time the response is monitored with blood work and vaginal ultrasound exams to follow the growth of the follicles.
Once there has been a good response and the follicles are mature, plans are then made for the egg retrieval, performed at our Waltham Center. The procedure is completed in less than 20 minutes under a light anesthesia. Under vaginal ultrasound guidance, a small needle is inserted into the follicle and the fluid is removed. All follicles are aspirated and the fluids are then passed over to one of our embryologists to identify the eggs under the microscope. Later that day, all of the eggs are frozen and then stored in liquid nitrogen tanks. Depending on the number of eggs available to freeze after the first cycle, some women elect to undergo an additional cycle to freeze even more eggs.
What the Future Holds
In the future when a woman decides she wants to get pregnant, she should try on her own initially. If pregnancy has not occured after 6 months, then she should follow-up with a reproductive endocrinologist. A fertility evaluation involving several tests will be performed to get a better understanding as to why pregnancy hasn’t occured. After reviewing the test results and taking the woman’s age into consideration, the doctor will discuss the best treatment option including intrauterine inseminations, IVF or using the previously frozen eggs.
How Frozen Eggs are Used to Achieve Pregnancy
In order to get the lining of the uterus ready for an embryo, estrogen pills and vaginal progesterone are used. The eggs are then thawed ~ the average survival rate for each egg is 90%. The eggs are then inseminated with a technique called ICSI, whereby a single sperm is injected into the egg. Approximately 70% of eggs will fertilize. Then the embryos are transferred into the uterus (this is a simple procedure, no anesthesia is required, and any remaining good quality embryos can be frozen for future use.
Success Rates
The success rate following the use of the frozen/thawed eggs is dependant on the age of the woman at the time the eggs were frozen (see graph above) and the number and quality of embryos that result. Depending on the number of embryos that are available, the woman may have the opportunity to undergo several cycles of treatment.