Egg Freezing
What is egg freezing?
Egg freezing (oocyte cryopreservation) allows unfertilised eggs to be stored for possible future use.
Why is egg freezing necessary?
Egg number and quality decline with age, particularly from the mid-thirties onwards.
This is because each woman is born with a specific number of eggs in her ovaries, which are gradually used up during her reproductive life. Over time, the number of eggs available in her ovaries decreases. When these eggs are exhausted, the woman enters menopause, which typically occurs around age 52.
The most important reason, however, why a woman’s fertility decreases with age is the significant decline in egg quality. Studies have shown that the period of peak fertility in most women is between ages 25-30. From age 30 to 35, there is a small gradual decline in fertility. From age 36 to 40, this decline is significantly greater, and after age 40, the decline accelerates sharply with each passing year. This means that a 42-year-old woman generally has one-quarter of the fertility she had at age 40.
Which women should consider egg freezing?
Egg freezing may be considered by women who wish to preserve the option of using younger eggs in the future. This desire may be related to social reasons, such as not being ready or able to try for pregnancy at present. Another important reason for egg freezing is the pursuit of professional goals that make starting or expanding a family before age 36 difficult. Egg freezing allows women to reduce the pressure of their biological clock and choose the right time for motherhood.
Another important category of patients who should consider egg freezing for fertility preservation are those with medical reasons. Women diagnosed with diminished ovarian reserve at a relatively young age, without the immediate prospect of starting a family, can freeze their eggs to give them the possibility of creating a family in the future even if they enter premature menopause. Egg freezing may also be considered by women who are about to have ovarian surgery that could reduce the number of available eggs, for example before removal of an endometriosis cyst (“chocolate” cyst/endometrioma).
Women diagnosed with cancer should be offered timely information about fertility preservation through egg freezing when clinically appropriate. This is because cancer treatment is often particularly harmful to the ovaries and a woman’s fertility, either through chemotherapy or through radiotherapy. At the same time, a cancer diagnosis often necessitates postponing plans to have a child, usually for 3-5 years. In these circumstances, timely fertility-preservation counselling can help patients decide whether egg freezing is appropriate for them.
What is the egg freezing process?
Egg freezing includes the following stages:
- Initial assessment by a Fertility/Reproductive Medicine specialist with medical history, clinical and laboratory examination related to fertility, and discussion of the treatment plan for egg freezing
- Ovarian stimulation with medications to develop and collect more than one egg. Collecting multiple eggs ensures maximum effectiveness of egg freezing, and the modern stimulation strategy includes attempting to collect as many eggs as possible using patient-friendly stimulation protocols. Typical ovarian stimulation usually lasts 10-12 days (8-14 days).
- Monitoring: During stimulation, 2-3 visits to the Fertility/Reproductive Medicine specialist will typically be required for hormonal testing (blood draw) and ultrasound examination (transvaginal ultrasound). These tests allow the doctor to monitor the normal progress of ovarian stimulation and estimate the number of eggs to be retrieved.
- Completion of stimulation and egg retrieval: When the doctor observes on ultrasound a group (usually >2) of follicles of adequate size (usually ≥17mm in mean diameter), they proceed with final oocyte maturation by administering a final injection. Egg retrieval is usually performed 36 hours (34-38 hours) after this injection. Egg retrieval is usually performed under sedation to minimise discomfort., and usually lasts 20-40 minutes. It involves retrieving eggs under ultrasound guidance through a relatively thin needle that passes through the thin vaginal wall and aspirates fluid from each follicle. After egg retrieval, patients may feel some discomfort similar to “period pain” and may have a small amount of vaginal bleeding. These symptoms usually resolve completely within 24-48 hours.
- Egg maturity assessment and freezing: After egg retrieval, within 2-3 hours, the collected eggs are checked for maturity in the laboratory, and those found to be mature are cryopreserved. Eggs can remain cryopreserved for an initial period of 5 years, which can be renewed for an additional 5 years.
How is pregnancy achieved using frozen eggs?
When a woman wants to use her frozen eggs to achieve pregnancy, the process is generally as follows:
- Assessment of fertility and the woman’s general health by a fertility specialist at the time she wishes to conceive and planning of next steps. For example, assessment of the uterus and endometrium may be performed, as well as other factors (e.g., presence of high blood pressure, diabetes, obesity, etc.) that may affect becoming pregnant and pregnancy health. If there is a partner, male fertility is also assessed, e.g., with a semen analysis. If there is nothing to prevent treatment, the most suitable time to thaw and fertilise the eggs is then planned. Finally, every woman planning to conceive (whether naturally or with assistance) should take necessary supplements before conception (e.g., folic acid).
- Egg thawing and fertilisation: Egg thawing is usually performed on a specific day of the woman’s cycle (the day of her ovulation). For this purpose, cycle monitoring with blood tests and gynaecological ultrasound is usually required. On the day of egg thawing, the surviving eggs are fertilised in the laboratory using ICSI with sperm from a partner or donor. After 16–18 hours, we will know how many eggs have fertilised successfully; these are then cultured in the laboratory.
- Embryo culture, embryo transfer, and cryopreservation of suitable embryos: The fertilised eggs are now considered embryos and are cultured in the laboratory usually for 5-6 days. The purpose of culture is to reveal which embryos have the potential to result in pregnancy, as many of the initial embryos will stop developing in the first hours/days of culture.
On the 5th day of culture, the number of surviving embryos and their quality are assessed. The embryo or embryos selected for transfer will be placed in the uterus through a simple procedure that usually takes about 15 minutes. The woman will know if she is pregnant approximately 10-14 days after embryo transfer. If on day 5-6 of embryo culture there are additional good quality embryos, these will be cryopreserved for future use (either if the first embryo transfer is unsuccessful or if the woman wishes to attempt another pregnancy in the future).
What determines the success of egg freezing?
The success of egg freezing depends primarily on two factors.
- The number and quality of eggs: It is now known that the more eggs that have been cryopreserved, the greater the probability of having a child from this procedure. Although there can never be absolute certainty that pregnancy will result from egg freezing, studies have shown that cryopreserving a larger number of eggs results in a higher probability of success. For this reason, many women will choose to undergo the procedure more than once to increase the probability of success. Perhaps an even greater impact on the probability of success than the number of eggs is their quality. This quality is primarily determined by the woman’s age and is considered excellent between ages 25-32, with a gradual decline after age 32. This means that a woman who has frozen 10 eggs at age 30 has approximately the same success probability as a woman who has frozen 30 eggs at age 37. Other factors that determine egg quality are genetic factors, smoking, obesity, etc.
- The laboratory methods used for egg cryopreservation (freezing) and thawing: As egg cryopreservation is a technology that relies on successful application of laboratory techniques, outcomes also depend on the quality of the embryology laboratory and the experience of its staff. The application of modern cryopreservation methods such as vitrification ensures the best possible results with egg survival probability exceeding 80% and usually reaching 90-95%.
Are there risks from the egg freezing procedure?
Egg freezing is generally safe when performed by an appropriately trained fertility team.
Ovarian hyperstimulation syndrome (OHSS) is a recognised complication of ovarian stimulation. Modern protocols substantially reduce, but do not eliminate, this risk . The egg retrieval procedure carries risks of bleeding, bowel injury, and pelvic inflammation, which are again extremely small when the procedure is performed by experienced fertility/Reproductive Medicine physicians.
A common question from patients undergoing ovarian stimulation is whether taking medications will increase the probability of developing some form of cancer in the future. This question has received considerable attention from the medical community, and most of the studies carried out are reassuring, as they do not support such an association.
Finally, another concern of patients undergoing egg freezing is whether retrieving these eggs will reduce their future fertility, i.e., lead to a significant reduction in the eggs they have in their body. The answer to this question is that retrieving these eggs does not affect at all the number of eggs they would have available in their ovaries in subsequent years and therefore does not negatively affect the future fertility of these women.
How many eggs do I need to ensure my future fertility?
It is important to emphasize that the term “ensure” is not correct and often creates a false sense of security in patients, as there can never be certainty of 100% success of the method regardless of how many eggs are cryopreserved.
A more correct and realistic approach is estimating the probability of having one or more children based on the number of mature eggs frozen by a woman of a specific age.
For example, a 35-year-old woman who freezes 12 eggs has approximately a ~75% probability of having one child, ~39% of having two children, and ~14% of having three children. If she has frozen 20 eggs, she has approximately a ~90% probability of having one child, ~66% of having two children, and ~38% of having three children.
On the other hand, a 39-year-old woman who freezes 12 eggs has approximately a ~45% probability of having one child, ~11% of having two children, and ~2% of having three children. If she has frozen 20 eggs, she has approximately a ~63% probability of having one child, ~25% of having two children, and ~7% of having three children.
If you want to calculate the probability of having a child based on your age and the number of mature eggs you have or plan to cryopreserve, you can use the egg freezing calculator that can predict these probabilities based on internationally published data.