Oocyte Cryopreservation (Egg Freezing)

Sara Mucowski, MD
October 19, 2020
Oocyte Cryopreservation (Egg Freezing)

The most basic reproductive biology includes the meeting of a man’s sperm and a woman’s egg, or oocyte, to make an embryo. What many women don’t realize is that while men continue to produce new sperm long into older age, women are born with all the eggs they will ever have, roughly 2-7million, and this number steadily declines over time. In fact, at puberty a woman has only 300,000 eggs remaining. Thereafter, every month (whether you’re on birth control or not) several eggs compete to be the lucky one that gets to ovulate in hopes of meeting that special sperm, and all of the competing eggs that didn’t ovulate are lost, further reducing the number of available eggs. As we age, there are less and less eggs competing each month, and of those available to compete, there are fewer genetically normal eggs. In short, as women age, both the quality and quantity of eggs diminish.

Oocyte cryopreservation, commonly referred to as “egg freezing”, is the process by which eggs are harvested from a woman’s body and frozen for later use. Once harvested eggs are frozen, they are presumably good indefinitely, suspended in time until the women chooses to thaw them for use. Statistically, the quality and quantity of eggs starts to diminish at a faster rate around age 35 when a woman is considered “advanced maternal age”. This is not a steadfast rule; some women will have egg decline earlier and some will experience it later, but all women experience it eventually. Changes in a woman’s menstrual cycle are often a later sign of this decline in egg reserve.

Because the quality and quantity of eggs decreases as a woman approaches age 35, freezing eggs at a younger age is ideal. However, freezing eggs at a very young age for the sole purpose of electively delaying childbearing may prove to be a waste of time and money, since a woman may get pregnant the old fashioned way without ever using their frozen eggs. For women who have invested in long educational and career goals and haven’t chosen to have a child before the age of 35, freezing younger healthy eggs provides a way to potentially prolong their reproductive years. Many other women may find egg freezing a desirable way to preserve their fertility, including women faced with cancer or diseases whose treatment may impair fertility, as well as single and divorced women who don’t want to raise children alone and have yet to find the elusive Mr. (or Ms.) Right.

The process of egg freezing is identical to that for IVF, or in vitro fertilization, without the fertilization part. After meeting with a doctor who specializes in Reproductive Endocrinology and Infertility (REI), a time will be determined both by your personal schedule and your menstrual calendar to start the process. You may take birth control or shots for a few weeks in preparation to synchronize your ovaries and their eggs. Afterwards, you will start stimulating your ovaries with hormonal injections to keep all the eggs growing that would normally be in competition that month. No more eggs can be stimulated than would otherwise be competing in any given month – that number is set by your body, and as of yet, there is no way to recruit more eggs to stimulate beyond what your body naturally offers.

Once you have decided on a schedule with your REI, stimulation with 2-3 hormonal injections per day to encourage growth and maturation the eggs begins, as well as to prevent you from ovulating prematurely. These injections last for roughly 10 days. During this time you will need to be seen by your doctor every 1-3 days to do blood work and have a vaginal ultrasound. Vaginal ultrasound is the best way to track the growth of the follicles, which a fluid-filled cysts that each contain an egg. Once your doctor determines it is time to harvest the eggs from the follicles, an injection is needed to “trigger” ovulation. The process culminates with a minor outpatient surgical procedure for “harvesting” the eggs that often takes less than 30 minutes. It is usually performed under a very light anesthetic; you are completely asleep and cannot feel or remember anything, but are breathing for yourself. The follicles are visualized with vaginal ultrasound and are pierced using a long needle, leaving no visible incision. The needle is connected to suction, which drains the follicles of all the fluid and cells, including the single egg inside. After you wake up, your doctor will tell you how many eggs were retrieved, and their maturity is assessed the next day. Only mature eggs will be frozen. Complications are very rare and most women are able to return to work the day after surgery.

Once the decision is made to utilize these frozen eggs, it is important to keep in mind that not every thawed egg will result in pregnancy. Just as with fresh eggs, not every mature egg that was frozen will fertilize after it is thawed. Of those that do fertilize after thawing, not every embryo will grow, and not every growing embryo will implant and result in a healthy baby. The good thing is that technology has and is greatly improving the rate of survival of eggs when thawed. Historically, many providers advocated embryo freezing over egg freezing for women wishing to preserve their fertility. However, with the currently improved thawed egg survival rates, women who freeze eggs can expect similar pregnancy rates to those using fresh eggs.

Many women are not interested in pursuing fertility preservation when it involves a known or anonymous sperm donor to create embryos through IVF. As a result, egg freezing is a valid alternative. If you have questions regarding fertility preservation, don’t hesitate to speak with a REI to help determine if you are a good candidate for egg freezing.

Sara Mucowski, MD

Sara Mucowski, MD

Dr. Sara J. Mucowski finished a 6-year combined Bachelor of Science/Medical Degree (BS/MD) program with Villanova University and Drexel University College of Medicine. After graduating with honors, Dr. Mucowski went to Galveston, Texas, where she completed her residency in Obstetrics and Gynecology at the University of Texas Medical Branch (UTMB). She then went on to complete a fellowship in Reproductive Endocrinology and Infertility at the University of Southern California (USC) in Los Angeles, CA. . She recognizes that every situation is unique, and requires treatment to be tailored individually to maximize success.

You can follow Sara on Instagram @saramucowskimd!

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