What is egg freezing?
A woman’s fertility is predominantly dependent on the quality and quantity of her eggs. A healthy woman has a finite number of eggs, which is at its maximum (6-7 million) before birth and continues to decline throughout life. As egg numbers and quality decline, chances of both natural conception and success through fertility treatment decrease significantly over 35 and this process accelerates over 40.
As the last 30 years the average age of women in their first pregnancy in the UK has consistently increased, egg freezing allows women the option of freezing their eggs when younger. This may offer her a better chance of a successful pregnancy in the future than using her older “fresh” eggs, which may be lower in both quality and quantity.
Egg freezing today involves “vitrification” which is a new rapid cryopreservation technique that minimises crystal formation and therefore limits damage during the freeze/thaw process. This has meant that egg freezing is a potentially viable option in preserving a woman’s long-term fertility.
Who should undertake egg freezing?
Patients may wish preserve fertility for several reasons:
- To delay child bearing (“social” egg freezing)
- To allow treatment of a medical condition which may affect future fertility
- To store eggs, sperm or embryos, before cancer treatment
Increasing worldwide data is suggesting that frozen eggs may be as effective in achieving pregnancy as fresh eggs and long term data on pregnancy risks such as preterm labour or birth defects shows no increase.
To maximize egg freezing as an “insurance” policy, a number of stimulation cycles may be required. Using fresh IVF eggs, approximately 15 eggs are collected in women <35 for every baby born, 20 eggs in women 35-40 and many more required in those over 40. If a woman is contemplating this it is ideal to freeze at as young an age as possible and aim for at least 20 eggs in storage.
How does egg freezing work?
An egg freezing cycle is similar to an IVF treatment cycle, however the eggs collected may then be frozen directly (vitrified) or fertilized and the embryos can be frozen.
Women undergoing an IVF cycle will be given fertility drugs to try and produce more than the one egg usually produced in each cycle. These stimulation injections are given daily subcutaneously (under the skin). You will be taught and how to do this before you start. A second type of medication given as a nasal spray or injection depending on the protocol is also provided to stop you releasing the eggs (ovulating) before they are ready for collection.
Over a period of about two weeks, whilst taking these injections you will be scanned and have blood tests daily or on alternate days depending on your protocol. It is important to monitor the development of the follicles (the small collections of fluid where eggs develop within the ovary). This will help to correctly plan the day of egg collection, and also enable us to increase/decrease the doses of medicine depending on your response to treatment. This will help reduce the side effects of medication and optimize your chances of success.
When the scans and blood tests show that the eggs are ready for collection. A final hormonal injection of human Chorionic Gonadotrophin (hCG) is given approximately 36 hours pre-operatively. This stimulates the eggs to reach maturity.
The eggs are collected by ultrasound guided vaginal aspiration of the follicles. In the aspirate of the follicle the embryologist should be able to identify an egg. It is difficult to determine the number of eggs that will be collected until collection procedure. In rare cases no eggs are collected.
To minimize discomfort this is usually performed under light general anaesthetic or sedation.