Egg freezing is often referred to as fertility preservation because it allows a woman to preserve her fertility, i.e. the chance of conceiving a child with her own eggs, until a later point in her life when she is ready to have a child. Egg freezing can be performed for medical or social reasons.
Advances in cryopreservation (freezing) techniques for eggs have dramatically improved the survival rate and egg freezing provides women the opportunity to store their eggs until desired for pregnancy.
Recent studies indicate the pregnancy rate for IVF/ICSI using eggs frozen by the new vitrification method (see below for further details) are comparable to those of fresh eggs. Currently, we can expect a freezing and thawing survival rate of over 90% for vitrified eggs.
The vitrification technique
Unlike sperm, which has been successfully frozen and used for many years, eggs contain a large percentage of water (~90%). The largest factor that determines whether or not an egg will survive being frozen and subsequently thawed is the formation of ice crystals from that water during the freezing process.
Historically, eggs were slowly cooled from room temperature down to -196 °C, the temperature at which they will be stored (the temperature of liquid nitrogen). During this cooling process the water in the eggs would form ice crystals. Such crystals can damage the cellular structure of the egg and result in the egg not being usable when thawed. The freeze and thaw survival rate with the old method was in the range of 30%, which is not very encouraging.
Recent developments in the field have allowed our laboratory to adopt a new technique called vitrification. In this process the eggs are first prepared by being dehydrated and placed in specially formulated vitrification media (akin to using anti-freeze). The eggs are then rapidly cooled from room temperature to -196 °C such that the eggs are preserved in a glass-like state (hence ‘vitrified’). This technique has resulted in drastically improved freeze and thaw survival rates of over 90%.
Who might wish to freeze their eggs?
Women who wish to postpone childbearing (‘social’ egg freezing)
Many women are postponing their plans to have a family until well into their 30s. There are many factors influencing this decision; common reasons include other life plans, career or not having met “Mr Right” yet. Unfortunately, a woman’s fertility declines with age, and particularly rapidly after the age of 35, because she will start to run out of eggs. Hence, a woman planning to delay having a family can increase her risk of age-related infertility. Therefore, a woman wishing to delay having a family could consider freezing her eggs and thereby preserving her fertility until such time as she is ready to have a child. Similar to IVF treatment, the age at which a woman freezes her eggs is an important factor in her success rate for achieving a pregnancy using those frozen eggs later in life. At HSFC, we advise women considering social egg freezing to begin treatment preferable in their twenties and ideally before their 38th birthday. Also, we would advise patients that egg freezing should be considered a back up plan and should not withhold them planning their pregnancy within a normal childbearing age because there is no guarantee that frozen eggs will provide a successful pregnancy in future.
Women considering cancer treatment or other treatment that may cause them to lose their fertility (e.g. chemotherapy or radiotherapy)
Permanent loss of ovarian function can occur from other medical treatments, including chemotherapy, radiotherapy or radical surgery. Egg freezing prior to commencing such treatment will preserve fertility to a later date when their disease is in remission. The possibility of preserving your fertility has become more important with the ever-increasing survival rates for cancer.
Women with increased risk of premature ovarian failure
Any woman who suffers from certain medical conditions that may cause premature ovarian failure, such as severe endometriosis or recurrent ovarian cysts, may wish to consider freezing her eggs as a form of fertility preservation.
Women with increased risk of early menopause
Premature menopause is often genetically inherited. Any woman who is aware that her mother, aunt or maternal grandmother started their menopause early (i.e. in their 20s, 30s or 40s) may consider egg freezing as a form of fertility preservation.
Women who wish to undergo gender reassignment
Women wishing to undergo a gender reassignment may consider freezing their eggs in order to preserve their fertility ahead commencing hormone therapy or surgery.
Women who have ethical or moral concerns about freezing embryos
Some couples having IVF may have ethical or moral concerns over freezing embryos and such couples may find egg freezing an acceptable alternative treatment.
How long can I store my eggs?
Eggs frozen for medical reasons can be stored for up to 55 years. Eggs frozen for social reasons can be stored for up to 10 years, however, this period can be extended to a maximum of 55 years if the woman or her partner is likely to become infertile during the original storage period.
The egg freezing procedure
A woman considering egg freezing will first need to have a fertility check-up, including hormone blood tests and ultrasound scans at the appropriate time in her cycle in order to determine if the treatment is a good option for you. If you decide to proceed with egg freezing, you will need to be screened for infectious diseases before treatment. You will also meet with one of our nurses to complete some consent forms for treatment. The nurse will also show you how to self-administer the medications that you will require for treatment.
When the preparations are complete, you will be asked to call on day 1 of your period to attend the clinic for a scan within the next few days. After the scan, you will be asked to start daily injections to stimulate growth of follicles in your ovaries. Growth of your follicles will be closely monitored by ultrasound scans and blood tests (every 2-3 days). Once the follicles have grown suitably, you will be asked to take a ‘trigger’ injection to stimulate final maturation of your eggs.
At this point you will be ready for your egg collection procedure. The eggs are collected using a needle inserted through the vagina under ultrasound guidance. The procedure typically takes less than 30 minutes. The procedure is performed under mild intra-venous sedation: you will not feel any pain during the procedure. Since you are receiving sedation, you will be monitored after the procedure before being discharged. You will need to be escorted home and you will be unable to drive or operate heavy machinery that day. We would advise you to take rest for the day.
The eggs are prepared for vitrification by being dehydrated and placed into vitrification media. The eggs are vitrified by rapidly freezing to -196 °C in liquid nitrogen and kept in liquid nitrogen until needed.