What Is Egg Freezing, How Does It Work and How Long Can Eggs Be Stored?

Egg freezing, or oocyte cryopreservation, collects a woman's eggs and stores them in liquid nitrogen at minus 196 degrees Celsius, so they can be thawed, fertilized and transferred as embryos at a later date. The eggs do not age while frozen, which is the point of the procedure: it preserves eggs at the age they were collected. The process takes about two weeks from the start of stimulation to egg retrieval. How long eggs may legally be stored is set by national regulation and differs by country, so it is a question to put to the clinic directly.

What is egg freezing?

Egg freezing preserves unfertilized eggs for future use. Eggs are collected from the ovaries after a course of hormone stimulation, then frozen rapidly and held in liquid nitrogen at minus 196 degrees Celsius. At that temperature the biological processes that would otherwise age or degrade the cells effectively stop.

When you are ready to use them, the eggs are thawed and fertilized with sperm in the laboratory to create embryos, and an embryo transfer follows. Egg freezing is therefore the first half of an IVF cycle, carried out and paused. It is not a separate route to pregnancy.

Does age at freezing matter?

It is the most important variable. Both the number and the quality of a woman's eggs decline with age, so eggs frozen earlier are generally better placed than eggs frozen later. That is the whole logic of the procedure.

The Human Fertilisation and Embryology Authority notes that most patients under 38 have around 7 to 14 eggs collected in a cycle, though this varies with individual ovarian reserve. It also advises that because egg freezing success statistics are based on relatively small numbers, a more useful guide to your likely outcome is the success rate for fresh IVF cycles using a woman's own eggs in her age band. Ask for that figure rather than a general one.

Who is egg freezing for?

• Women who are not ready to have children yet and want to preserve the option while their eggs are younger.
• Women about to undergo medical treatment that may affect fertility, including chemotherapy, pelvic radiotherapy or ovarian surgery. Freezing is usually arranged before treatment begins, so this is time-critical.
• Women with a condition or family history suggesting ovarian reserve may decline early.

How long can eggs be stored?

Two separate questions sit inside this one. Biologically, eggs held correctly in liquid nitrogen are not thought to deteriorate with time in storage, and pregnancies have followed long periods of storage. Legally, the maximum storage period is set by national regulation and varies considerably between countries, as do the consent requirements for keeping eggs in storage.

In Thailand, section 42 of the ART Act delegates the storage rules to the Medical Council rather than fixing a period in the Act itself, so ask us what period currently applies, what happens at the end of it, and what you need to sign to keep the eggs in storage.

What are the steps in the egg freezing process?

1. Consultation and assessment. Medical history, physical examination, and blood tests to check hormone levels, screen for infection and assess ovarian reserve.
2. Ovarian stimulation. A course of hormone injections encourages the ovaries to mature several eggs rather than the single egg of a natural cycle.
3. Monitoring. Ultrasound scans track how the follicles are developing and the dose is adjusted accordingly.
4. Trigger injection. Once the follicles reach the right size, a trigger injection completes egg maturation and sets the timing for collection.
5. Egg retrieval. Eggs are collected through the vagina under ultrasound guidance, with anesthesia. It is a short procedure and you go home the same day.
6. Freezing. The eggs are frozen by vitrification, a rapid freezing method, and stored in liquid nitrogen.

We at Millennium IVF Clinic carry out egg freezing at our Bangkok clinic. You can arrange a consultation with our team to discuss whether it applies to you, and our egg freezing page covers the service in more detail.

Frequently asked questions

Does egg freezing guarantee a baby later?

No. Freezing preserves eggs; it does not guarantee that they will fertilize, develop into viable embryos or result in a pregnancy. The HFEA advises looking at IVF success rates for your age band to understand the realistic picture.

How many eggs should be frozen?

There is no single number. It depends on your age and ovarian reserve, and some women undergo more than one collection cycle to bank a reasonable number. Our article on how many eggs to freeze covers this.

Is egg freezing the same as embryo freezing?

No. Egg freezing stores unfertilized eggs, so no partner or donor sperm is needed at that point. Embryo freezing stores eggs that have already been fertilized. Our article on egg freezing or embryo freezing compares them.

Is egg retrieval painful?

The retrieval is typically carried out under sedation or a light general anesthetic, so you should not feel the procedure itself. Some cramping and bloating afterwards is common. We will confirm what will be used for you when you consent to the procedure.