A Fertility Specialist Explains Everything You Need to Know About FET

What is FET?

A Frozen Embryo Transfer (FET) cycle is the process in fertility treatment whereby frozen embryos are used in IVF. The frozen embryos that are used are either from a previous cycle or from the same cycle (called a “freeze-all cycle”). A freeze-all cycle is especially useful for women who are at risk of ovarian hyperstimulation syndrome (OHSS) or using donor eggs, as they can take a break from the hormones and have a FET in their own time. The frozen embryo is thawed and monitored in a laboratory to assess its viability for transfer.

Before a FET, fertility medication is used to prepare the uterus for embryo transfer and implantation. In a fresh embryo transfer the ovaries are stimulated – in a FET, they are not.

When would someone have a FET vs. fresh embryo transfer?

Some people may have a FET instead of a fresh ET for medical reasons. Various factors can affect the success of implantation (and a FET might be advised), such as the patient being unwell, having raised levels of progesterone, having a thin endometrium prior to their fresh ET, or if there is a high risk of OHSS. If a high number of eggs are collected, fertility specialists may recommend some eggs are frozen for future fertility treatment. Other reasons for having FET would be following PGT-A testing, or if there are embryos remaining from a previous cycle. 

Male- or female- factor fertility issues can affect embryo quality and the subsequent number of embryos that are suitable for freezing, however female factors, such as a polyp or fibroid within the uterus may need to be treated or removed prior to having an embryo transfer. In this situation, fertility specialists might recommend freezing eggs or embryos whilst the polyp or fibroids are treated.

Suitable embryos from IVF or ICSI cycles can be used for FET; your fertility specialists and embryologists will be able to advise on embryo quality and suitability for freezing.

What to expect from a FET?

Depending on your medical history and menstrual cycle, you may have a “natural FET cycle” without fertility medications, or you may require some hormone medications to help prepare the lining of your womb for embryo transfer. Either way, you will need to have an ultrasound scan at the start of your period, to assess your womb lining and ovaries prior to starting your fertility treatment cycle. You will then need at least one subsequent scan to ensure the lining of your womb is optimal for your embryo to be transferred. The embryo transfer procedure is usually very quick and pain-free, similar to a cervical smear test. You will be awake and asked to have a full bladder – this can be uncomfortable but shouldn’t be painful.

What is the timeline for a FET?

This will depend on your protocol, but you will usually have 2-3 weeks of medication or monitoring of a natural cycle until the actual embryo transfer. The ET is usually 2 -3 weeks after the start of your period, with your pregnancy test usually 11 days after this. So the entire process from start to pregnancy test is about 4 weeks.

How do I prepare for a FET?

This depends on which protocol you are on but you will need to make sure all the correct consent forms are filled in (your fertility clinic will be able to help with this) and you have the time available for investigations, monitoring and fertility treatment. FET cycles are sometimes considered less “strenuous” than fresh cycles, as the fertility medication does not stimulate the ovaries, only the uterus to prepare for transfer and implantation.

As with all fertility treatments, it’s important to ensure you aren’t smoking, are a healthy weight for your height and minimise alcohol and caffeine intake. Fill gaps in your fertility-friendly diet by taking a fertility supplement with folic acid and Vitamin D.

Does implanting more than one embryo increase the likelihood of pregnancy?

Yes, but it doesn’t guarantee a pregnancy as pregnancy is mostly determined by embryo quality. Transferring more than one embryo increases your chance of twin pregnancy by about 25%, and multiple pregnancies put the pregnancy at a higher risk than a single pregnancy – this is why it is generally not recommended to transfer more than one embryo. Similarly, Your fertility specialists will suggest the best number of embryos to be transferred, depending on the embryo quality, and your medical history.

What are the success rates of FET?

How can I increase the chances of success of my FET?

• Take all your fertility medication on time, as indicated.
• Try to not be too stressed (yoga and other relaxation techniques may help)
• Maintain a healthy diet, regular exercise and have a healthy weight for your height.
• Minimise your alcohol and caffeine intake and do not smoke.
• Take the recommended fertility supplements, including folic acid and vitamin D (this applies to men, too).

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