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The process of frozen embryo transfer (FET): a detailed overview

In recent years, fertility treatments have evolved to become more successful and less invasive thanks to the advancements of modern medical technology. At the Bristol Centre for Reproductive Medicine, we offer a wide range of fertility treatments to support you on your fertility journey.

A frozen embryo transfer (FET) is a unique type of treatment that involves freezing and storing embryos before transferring them to your womb. In this guide, we take an in-depth look at the process of FET, including the different types, success rates and what to expect during your appointment.

At BCRM, we want to empower you with fertility treatment knowledge so you feel confident and secure in your choice of treatment.

What is frozen embryo transfer?

The first part of a frozen embryo transfer involves freezing your fertilised eggs. These are frozen on either day 5 or 6 of their development, once they have reached the blastocyst stage (the early development of an embryo).

The embryos are frozen using a process called ‘vitrification’, where they are placed into protective solutions at specific intervals and frozen in liquid nitrogen. Vitrification provides a higher chance of successful thawing and reduces the risk of damage during both the freezing and thawing processes. Once frozen, they are sealed, labelled and stored until you are ready to try and become pregnant.

Often, the embryos selected for freezing come from previous cycles of in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI). Freezing any remaining fertilised embryos after either of these treatments means you will not need to have further eggs retrieved should you decide to undergo fertility treatment later on.

When you decide to undergo FET, the embryos will be thawed carefully. Next, they will be inserted into your uterus through a catheter (a thin flexible tube). However, only one or two embryos will be thawed and transferred to reduce your risk of a multiple pregnancy.

Types of FET

There are two different types of FET. First, there is natural cycle FET. This type is recommended if you have a regular menstrual cycle and can predict ovulation. Your thawed embryos will be transferred after you have a positive ovulation test.

The second type is programmed medicated cycle FET. This is where you take hormone medication to help grow the lining of your uterus until it’s ready for the embryos to be transferred.

You will then take progesterone pessaries to support the implantation and development of your baby until you are 12 weeks pregnant. This type is often recommended for women whose menstrual cycles are disrupted or unpredictable due to health conditions or unknown reasons.

Does freezing harm your embryos?

Freezing does not harm your embryos. At BRCM, our survival rate for high-quality embryos is over 97%.

The frozen embryo transfer process

The process of an FET is relatively simple and considerably less invasive than other fertility treatments.

Preparing for FET

If you are undergoing a programmed medicated FET, you will have a blood test and a vaginal ultrasound to check if your endometrium (the lining of your uterus) is thick enough. Once it is, the procedure can be carried out.

On the day you are scheduled for your treatment, we will take the selected embryos out of storage and rapidly warm them up. We also gently wash them to support their recovery during the process.

In the following hours, the thawed embryos will return to their original state and become ready for use in treatment. We will thaw enough embryos to give you the highest chance of pregnancy and the lowest risk of a multiple pregnancy.

During and after FET

A frozen embryo transfer takes up to 30 minutes to complete. First, a speculum is inserted into your vagina. Next, the catheter containing the embryos is inserted into your uterus. A small amount of fluid inside the catheter helps the embryos to be released. The catheter and speculum are then removed and the procedure is complete.

After your embryos have been transferred, you will be allowed to rest for however long you need. As the procedure isn't highly invasive and no anaesthetic is used, you may not need much time before you feel ready to go home.

It's important to remember not every FET will be successful, even if you do everything right. However, at BCRM, we will do everything we can to support you on your fertility journey and provide you with access to the treatments you need.

Potential risks of an FET

There are some potential risks associated with undergoing an FET. These can include:

  • The lining of your uterus doesn't thicken enough, even with oestrogen medication

  • Unexpected ovulation, meaning the window for transferring has been missed

  • Excess fluid that's naturally built up in your uterine cavity – this can reduce the chances of implantation

At BCRM, we take every precaution and will monitor you before your FET to ensure your body is ready to give you the highest possible chance for success.

FET success rates

The success rates for an FET are comparable to that of the use of fresh embryos. Success rates of an FET can depend on various factors though such as your age – both when the embryos were frozen and when they were transferred.

At BCRM, our success rates can be seen in the below table.


BCRM success rate

National average success rate

Under 35

53% (based on 197 embryos transferred)


35 - 37

38% (based on 114 embryos transferred)


38 - 39

32% (based on 59 embryos transferred)


40 - 42


Not available



Not available

Data obtained from HFEA website IVF/ICSI

We have a much higher rate of success than the national average for FET, so you can feel confident in your decision when choosing us for your frozen embryo transfer.

Book an appointment with BCRM

FET fertility treatments can help you to start or grow your family and, at BCRM, we offer you exceptional, personalised care throughout.

Our dedicated team of fertility specialists ensure you are fully informed and provide you with an unparalleled level of care and understanding.

If you would like to discuss your fertility treatment options or book a frozen embryo transfer, you don't need a referral to start your treatment with us, so get in touch with our team to get started. We will ensure you receive the care and support you deserve throughout your fertility journey.