Egg and Embryo Freezing, Preservation and Thawing
Women, particularly single women, who delay childbearing due to personal circumstances now have the option of freezing their own eggs so that these may be fertilized and implanted at a later date. This significant step forward in fertility treatment enables women to take advantage of their body’s fertility at a time when eggs are at their healthiest.
Women have on average about 600,000 eggs at birth, and this supply diminishes at a rate of about 1,000 per month, right from the day she is born. This decline is part of the natural aging process, and is commonly referred to as a woman’s biological clock. The loss of oocytes from the ovaries is relentless and continues even in the absence of menstrual cycles, and even when women are pregnant, nursing or taking oral contraceptives. The rate at which eggs are lost is also thought to accelerate during the late 30’s and early 40’s so that women generally lose the natural ability to have children around their mid 40’s. Importantly, egg quality also diminishes with time, with miscarriages and chromosome defects becoming more common with later age at pregnancy.
Previously, a woman not ready for parenthood and wishing to use her own eggs had the option of harvesting her own eggs through IVF and then fertilizing these eggs with partner or, in the case of women that do not have a partner, anonymous donor sperm. The resulting embryos would then be frozen and implanted at the appropriate time.
Embryo freezing, as well as third party parenting options such as egg donation or adoption still are viable and attractive options for many older would-be parents. For younger women who know in advance that they may want to extend their fertility potential, egg or oocyte freezing (also called fertility preservation) provides the ability to preserve a woman’s own genetic material until such time as she is ready to pursue parenthood.
Pacific Fertility Center has been freezing eggs since 2007 when we first embarked on a project freezing donor eggs. Since then, we have performed many cases of egg freezing and the number of patients coming in for oocyte freezing is steadily rising. While once considered an experimental procedure, success with egg freezing has led to widespread acceptance. It is now being performed in IVF centers around the world.
When talking with interested patients, we do recommend that women carefully consider this option before embarking on it. For instance, some women may meet a subsequent partner and never use their banked eggs, while some may rely on these banked eggs for a future pregnancy but their particular eggs might not result in a viable pregnancy. Unfortunately, there is no way to guarantee or know what the outcomes will be at the time of thawing the eggs. We suggest a detailed discussion about fertility preservation with your PFC physician before choosing this option.
Preparing for Egg Freezing
The egg freezing process begins with In Vitro Fertilization (IVF) so that multiple eggs may be produced for freezing. A high number of eggs provides ample opportunities for fertilization and pregnancy later on.
Women interested in freezing their own eggs will first be asked to undergo a series of fertility tests to assess their reproductive potential and readiness for the IVF process.
- Initial evaluation of ovarian reserve. The first step for those wishing to freeze their own eggs is a consultation with one of PFC’s reproductive endocrinologists. One of the major considerations in fertility preservation is the age of the woman. Is the patient still young enough at the time of freezing that they have a high likelihood of future success using these eggs? How many eggs might be needed to help ensure future success? In general, the older the patient at the time of egg freezing, the lower the rate of future success. This is true for all IVF patients, and not just for those freezing oocytes, because oocyte quality diminishes with maternal age. Therefore, for older women we might suggest more than one cycle with oocyte freezing to increase the number of eggs banked and theoretically, the odds of future success.
Your doctor will also conduct a number of tests to determine your potential for creating a high number of eggs for freezing.
FSH (follicle stimulating hormone) and Estradiol and AMH Blood Testing (indirect measure of ovarian reserve). As part of the body’s normal reproductive cycle, a hormone called FSH recruits eggs to grow in the ovaries. High FSH levels in a woman indicate that the body is working extra hard to grow eggs, which can in turn be an indication of low egg numbers in the ovaries. This is called diminished ovarian reserve or DOR. A lower (or normal) FSH value indicates a greater potential for creating a substantial number of eggs for freezing.
Women having their FSH levels checked must have it done on day 2 or 3 of the menstrual cycle when the eggs are being recruited. Estradiol is also measured at the same time as a means of making sure that the FSH level is truly indicative of ovarian reserve. Estradiol comes from the granulosa cells surrounding the growing oocytes and this hormone actually suppresses FSH once oocyte growth has started. So if FSH is measured say on day 3 and Estradiol is already at a high level, the FSH value will have started to drop and will not be an accurate measure of ovarian reserve. A lower estradiol value suggests that oocyte growth has not yet started and we would therefore expect FSH to be at its highest level. The highest level for a given patient is what the test aims to measure, and measuring estradiol at the same time makes sure that we get that number.
Antral Follicle Count (AFC) and Anti-Mullerian Hormone (AMH) (direct measure of ovarian reserve). Oocytes grow inside follicles, and the small developing follicles that exist in the ovary are called antral follicles. An antral follicle consists of an egg, several layers of estrogen producing granulosa cells that surround the egg, and a small pocket of fluid (or cyst, called a follicle). Antral follicles in the female ovary viewed with an ultrasound scan can indicate a woman’s potential to produce multiple eggs for freezing. The higher the antral count (AFC), the higher a woman’s potential to produce an adequate number of eggs to be harvested and frozen.
Anti-Mullerian Hormone (AMH), is a hormone produced by the ovarian follicles. Measurement of AMH hormone levels likewise serves to assess ovarian reserve. A higher AMH count indicates higher ovarian reserve and thus greater fertility potential. Because it is not dependent on where a woman is in her cycle, it can be an easier test to obtain and interpret.
- Consultation with a PFC Counselor. In addition to fertility testing, women are asked to meet with a Marriage and Family Therapist at our Northern California San Francisco Bay Area fertility center to discuss the risks and benefits of the egg freezing process. Because such fertility treatment is a financial as well as an emotional commitment, we want all patients to have a full understanding of this technology and their potential for success.
The Egg Freezing Process
This process involves steps similar to In Vitro Fertilization (IVF), beginning with a series of fertility enhancing medications to produce multiple eggs and then retrieving the eggs.
Fertility medications. The first step in this process is to generate multiple eggs for retrieval. The patient’s physician will prescribe fertility medications to stimulate follicle growth and produce multiple eggs. Medications are injected subcutaneously (just beneath the skin) with a very fine needle. As always, our staff will counsel and instruct our patients on this process and are available throughout the entire process. This phase of treatment lasts approximately 10 days.
Ultrasound monitoring and lab tests. A patient’s physician will monitor them on a regular basis to assess follicle growth and the number of eggs they are producing. When eggs are determined to be mature and ready for retrieval, the patient will stop taking the fertility medication and receive one injection of hCG, a hormone that prepares eggs for ovulation. The hCG shot brings on the final phase of egg maturation, allowing the eggs to separate from the surrounding granulosa cells. The eggs would be naturally ovulated about 40 hours after the hCG shot, but we remove the eggs from the ovaries with a fine needle 4 hours before the predicted time of ovulation.
Egg retrieval procedure. This is a painless and relatively brief procedure, during which your doctor will use ultrasound guidance to gently retrieve eggs from the ovarian follicles. You will be under sedation and in the care of an anesthesiologist throughout the procedure. The retrieval is performed in our clinic and takes approximately 10 minutes; patients are able to resume normal activity shortly after the sedation has worn off.
Learn more about IVF and Egg Retrieval.
Egg preservation. The retrieved eggs are preserved through a rapid freezing process called vitrification. Eggs remain frozen until they are needed. The eggs may be kept frozen indefinitely so it is critically important that patients maintain annual contact with the clinic so we know the eggs have not been abandoned.
Using Frozen Eggs to Create Embryos
Thawing. When the patient decides they are ready to use their eggs, they will be thawed in the laboratory. The thawing is a rapid procedure performed on the day the eggs will be fertilized and must be synchronized with a woman’s cycle. Over 90% of frozen eggs, on average, survive the freeze-thaw process.
Fertilization. Thawed eggs are next fertilized in our laboratory using a procedure called Intra-Cytoplasmic Sperm Injection (ICSI) in which a single sperm is injected into each egg. Because the protein coat surrounding a frozen-thawed egg is hardened by the freezing process, ICSI rather than conventional mixing of eggs and sperm is required for successful fertilization. On average, about 70% of the injected eggs will be expected to fertilize normally.
Embryo culture. Once the eggs have been fertilized, they will remain in the laboratory for 3 to 5 days, growing and dividing, now called embryos. Not all fertilized eggs will divide to make nice embryos. The number that do survive and progress is again related to a woman’s age, as embryos have very abnormal chromosome numbers will tend to arrest their development within the first few days.
Embryo transfer. Prior to transfer, your doctor will discuss with you the number of embryos recommended for transfer. This number is based on a number of factors. The number we recommend to transfer will be made primarily based on the age of the egg provider at the time the eggs were frozen. For example, if the woman was 28 when eggs were frozen, a doctor might recommend only 1 embryo, but if she was 37, we would be likely to recommend 2 embryos. It is important to remember that it is your age at the time that the eggs were frozen is what matters, and not your age when you return to use these eggs. Your doctor will transfer the fertilized eggs (embryos) into the uterus using a small insertion catheter and under visualization with an abdominal ultrasound. The transfer feels similar to a Pap smear and does not require anesthesia. The procedure takes about 15 minutes (the transfer itself takes just 30 seconds). Learn more about the transfer procedure.
Re-freezing of excess embryos. According to the decision one makes with their physician, excess embryos may be re-frozen. Re-freezing the fertilized eggs (embryos) is safe and will make it possible to do another transfer if the first one does not work, or to have a future child if the first transfer does work.
Want to learn more about fertility preservation?
We invite you to schedule a fertility preservation consultation with the San Francisco Bay Area’s 'Top Docs' at Pacific Fertility Center®. We recommend that patients gather questions for the consultation beforehand, to make most of your appointment time. Some common questions include:
- How much does fertility preservation cost?
- What are the best fertility preservation options for someone in their 30’s?
- What fertility preservation technology is used at PFC?
- And much more… We’re here to answer your questions.
Pacific Fertility Center is conveniently located in the San Francisco Bay Area, near many local Northern California communities. Schedule a consultation and experience the 'art of conception' at Pacific Fertility Center® »