Common questions about egg freezing

What is ovarian stimulation?

Stimulation of the ovaries is recommended to collect multiple eggs. The stimulation requires hormone injections that contain follicles stimulating hormone (FSH) with or without luteinising hormone (LH), and are usually started at the very beginning of your menstrual cycle or an induced bleed. The dose and type of hormones is patient specific and depends on various factors, including age, body mass index, anti-Müllerian hormone (AMH) levels, antral follicle count (AFC), and response to previous hormone treatment.

Injections should be administered by yourself at the same time every day.

The injections are administered for a period of 10 to 14 days, depending on the ovarian response. Once your follicles have reached their optimal size, your consultant will prescribe the ‘trigger’ injection to ensure the eggs within your follicles mature and the eggs are ready for harvesting 34-36 hours later. 

How is the stimulation cycle monitored?

After 5 or 6 days of you taking the hormone injections, you will be having transvaginal ultrasound scans every 2 or 3 days. This is important to determine the development of the follicles, to alter the dose of the medications to ensure adequate response as much as possible, and to decide when to have the ‘trigger’ injection in preparation of the egg retrieval. Biochemistry (blood) tests are performed sometimes in conjunction with the ultrasound scans to better assess the response to the hormone treatment. 

How is the egg collection performed?

This procedure is performed in the theatre room, generally adjacent to the laboratory, and you will be given sedation medications via an intravenous line. An anaesthetist and nursing staff will be present in theatre together with the consultant. If necessary you may be given pain relief during the procedure or afterwards. 

The egg collection takes 15-30 minutes depending on the number of follicles available and the difficulty to access the ovaries. A fine needle, sliding into a guide mounted on the transvaginal ultrasound scan probe, is inserted through the vagina into the ovaries, and the fluid of each follicle is aspirated into a clear tube which is then passed to the embryologist to look for the egg. 

Very seldom absorbable stitches may be put inside the vagina at the end of the procedure, if there is a small area of bleeding. You will be able to resume normal activities the following day.

How are the eggs frozen?

After retrieval the eggs are washed and prepared for freezing using a technique called vitrification. Only mature eggs are frozen. Vitrification technique is used over slow freezing in most centres since there is no formation of ice crystals, so the risk of damaging the eggs during freezing is much smaller.

How are the frozen/warmed eggs fertilised when I want to use them?

The embryologist prepares the frozen eggs for warming in the laboratory. After the eggs have been warmed, the ICSI technique with either your partner’s or a donor’s sperm is used to fertilise the eggs that have successfully thawed. The normally fertilised eggs will then be kept in an incubator for a few days to assess embryo development and blastocyst formation before embryo transfer.

What is the survival rate of frozen eggs and the clinical pregnancy rate?

Egg freezing by vitrification has been around for over 10 years now. Data in the literature shows that about 80%  – 85% of all vitrified/warmed eggs will survive. This is much higher compared to slow freezing, which by comparison has a survival rate of between 55-65%.

The clinical pregnancy rate using frozen/warmed eggs depend on several factors such as patient’s age at the time of freezing, quality of the eggs and quality of the sperm used for fertilisation. However, the published reports show clinical pregnancy rates of up to 40%.

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