Frozen Embryo Transfer


Frozen embryo transfer (FET) is an assisted reproductive technique (ART) that forms part of assisted reproductive treatments such as in vitro fertilisation (IVF). Thanks to rapid advances in technology, frozen embryo transfer has made parenthood possible for many thousands of couples.


In this article, we look at what exactly frozen embryo transfer is, when it is utilised during fertility treatments, what the process entails, some of the considerations to take into account and where embryo freezing and frozen embryo transfers are available to couples facing infertility.

What is frozen embryo transfer?

An embryo is an egg that has been fertilised by a sperm. Because of the effectiveness of assisted reproductive treatments such as IVF, ICSI and PICSI – in which the eggs are fertilised with sperm outside the body in a lab – there are often more good quality embryos than are required for the immediate treatment cycle.

Thanks to modern technology called vitrification, it is possible to freeze or cryopreserve the spare embryos for use at a later stage, for example, if the first IVF cycle fails, or if the couple would like to have more children later. At a future time, a frozen embryo transfer can be performed in a simple, short procedure.

With modern freezing techniques and greater experience, results from the transfer of frozen and thawed embryos are now almost as good as those with fresh embryos.

When is frozen embryo transfer used?

Many couples undergoing IVF treatment choose to freeze their spare embryos for later use at a later stage. This, along with the current emphasis on achieving singleton pregnancies, has ensured that embryo freezing is now a fundamental part of every fertility clinic’s IVF programme.

Embryo freezing is also ideal for women at risk of hyperstimulation syndrome – a possible negative reaction to certain fertility medication.

Embryo freezing is also used if a woman has poor uterine lining (endometrium) at the time of a fresh embryo transfer – the embryos are vitrified instead and safely stored, ready to be transferred in a more favourable cycle.

The pregnancy rate for a frozen embryo transfer is similar to a fresh cycle. The average clinical pregnancy rate for a frozen embryo transfer is 46-52%.

What does the process entail?

Embryo freezing is done through advanced technology called vitrification – an ultra-rapid freezing method that yields better post-thaw survival rates and higher pregnancy and live birth rates.

Only good quality 5- or 6-day old embryos are vitrified and stored at -196ºC, relatively safe from damage. The recovering rate after warming is 98%.

Frozen Embryo Transfer or FET is the transfer of frozen embryos that have been vitrified in an earlier procedure. The process is not different from a cycle with fresh embryos.

A frozen embryo transfer can be performed in either stimulated or unstimulated cycles. During an unstimulated natural cycle, the embryo(s) are replaced in the uterus when implantation is most likely. With a stimulated cycle, you will take medication for the down-regulation of your ovaries to prevent any eggs from being released. After a scan on day two or three of your period, you will start taking medication to prepare your womb for the embryo transfer. If a second ultrasound scan at day twelve confirms that your endometrium is of the appropriate thickness, progesterone is introduced for five days and your transfer is booked.

The frozen embryos are warmed on the equivalent of Day 5 in either a natural or controlled cycle. Two hours after warming, the viability of the embryos can be determined. One or two embryos are transferred to the womb after an incubation period of 4 to 6 hours.

The embryo transfer itself is similar to a smear test and causes only minimal discomfort. A culture medium containing one or two embryos is loaded into a thin catheter with a syringe on the end. The doctor carefully guides the catheter through the vagina and cervix, and deposits the embryo(s) into the uterus, where implantation hopefully begins three to four days later.

Pregnancy testing is performed 10 to 12 days later with a sensitive blood assay for HCG hormone after a fresh or frozen blastocyst transfer.

Some considerations around frozen embryo transfers

One of the most important considerations around frozen embryo transfers is the possibility of multiple pregnancies.

While twins of even triplets may seem like a blessing to an infertile couple, in reality it involves many risks. Patients should be informed of risks associated with IVF multiple pregnancies and sign a consent form if more than one embryo is transferred.

At Medfem Fertility Clinic, we follow the guidelines provided by SASREG, the Southern African Society of Reproductive Medicine and Gynaecological Endoscopy, which protects the interests of the patients undergoing fertility treatment and represents specialists working in the field of reproductive medicine. SASREG embryo transfer guidelines are based on reviews of guidelines from other regulatory bodies such as ASRM and NICE and can be viewed here:

SASREG notes that multiple pregnancies can lead to both short and long-term health risks in ART offspring such as preterm delivery, low birth weight, pre-eclampsia, increased C/S deliveries and stillbirths, as well as adverse psychosocial effects in parents such as increased financial stress, anxiety, depression and marital dissatisfaction.

As a result, single embryo vitrification and transfer are used to reduce the risks.

When considering the number of embryos to transfer, these factors are included: the patient’s age; whether the eggs are the patient’s own or donated; whether the patient has a good ovarian reserve, or two or more good quality embryos available for freezing, and if there has been a previous successful IVF treatment cycle. Pregnancy risk factors such as increased BMI, increased age, comorbidities and previous poor obstetric history are also taken into account.

The guidelines note that for women older than 37, single embryo transfer is recommended, unless a top-quality embryo is not available for transfer, in which case two embryos can be transferred, provided there are no increased obstetric risk factors. For women between the ages of 37 and 39, unless the patient requests a single embryo transfer, the recommendation is the transfer of two embryos, provided there are no increased obstetric risk factors. For women aged between 40and 42, SASREG recommends the transfer of two embryos. SASREG further recommends that all embryo transfers should be performed under ultrasound guidance.

Is frozen embryo transfer for me?

Our team at Medfem Fertility Clinic has extensive experience in embryo freezing and frozen embryo transfer. We have been freezing embryos since 2007 and since then we have seen a considerable increase in embryo survival rates and substantially higher pregnancy rates after frozen embryo transfer procedures.

If you would like to find out more about frozen embryo transfer and whether it is a treatment option for you, we invite you to meet one of our fertility specialists at Medfem Fertility Clinic. We would be happy to answer your questions.

It is as simple as clicking here or phoning us on +27 (11) 463 2244.

Our team at Medfem Fertility Clinic believes in making world-class fertility treatments available for everyone. It is our joy and commitment to give you a positive outcome to your fertility journey, so you will have a fond memory of feeling empathy, caring and being part of the Medfem Fertility Clinic family.

We look forward to meeting you!


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