Information sheet - Frozen embryo transfer (FET)
What is an FET?

Following an in vitro fertilisation (IVF) cycle, surplus embryos may be frozen (cryopreserved) for the individual’s or couple’s future use. In accordance with the UK’s Human Fertilisation and Embryology Authority (HFEA) guidelines we are allowed to store embryos for up to ten years. Consent for storage will have been obtained at the time of your IVF treatment cycle.

Only good quality embryos will be frozen. Not all embryos will survive the freeze-thaw process.

There are two types of treatment cycle during which frozen embryos can be replaced: 

Natural cycle

If you have a regular menstrual cycle with normal hormone levels, it may be possible to have your embryos replaced during your natural cycle. It is, however, more usual at the Agora to be put on an artificial cycle with hormone replacement therapy (HRT).

It is important that embryos are replaced at the correct time during your cycle. This is determined using ultrasound scanning and follicle tracking. You would phone us on day 1 of your cycle to book the first scan which is usually performed on day 8 to 10 of your cycle, with alternate days scanning thereafter. You will be advised to check for a luteinizing hormone (LH) surge, using daily urine testing, once a lead follicle has been identified. Ovulation will be ‘triggered’ using an injection called Ovitrelle once your lead follicle has grown to 18mm diameter and your womb lining (endometrium) is 8mm or more unless the LH surge is detected.

The day on which embryos are thawed and replaced depends upon their age on the day of freezing:

  • A day 2 embryo is thawed and transferred three days following the LH surge or four days following Ovitrelle
  • A day 3 embryo is thawed and transferred four days following the LH surge or five days following Ovitrelle
  • A day 5 blastocyst is thawed and transferred six days following the LH surge or seven days following Ovitrelle
Artificial cycle (with down regulation)

For this procedure, you will be prescribed a medication known as GnRHa (Buserelin) as an injection once a day, from day 21 of your natural cycle. This ‘down regulates’ or ‘switches off’ some of your natural hormones, preventing the ovaries from naturally producing and releasing eggs.

We will ask you to phone the clinic to speak to one of the nurses on the first day of your next period, which should happen as normal. Your first scan, known as your ‘down regulation scan’, is scheduled on day two or three following this bleed. The lining of the womb (endometrium) is measured and, provided it is thin and no abnormalities are detected, you will be prescribed tables known as oestradiol valerate (Climaval or Progynova). These tablets are used to thicken the endometrium by replacing the hormone usually produced by the developing follicles within the ovary, and you will also continue to have the GnRHa injections.
After approximately 10 days of taking oestradiol valerate, you will be given a scan to check the endometrial thickness. Scanning continues on alternate days until this measures 8mm or more and, once the desired thickness is achieved, the GnRHa is stopped. We will give you progesterone pessaries (Cyclogest) or injections (Gestone) twice daily which will maintain the endometrial thickness. We advise you to take the pessaries rectally at this time until after the embryo transfer when they can be used either rectally or vaginally.
The transfer is scheduled four to six days after starting progesterone depending upon the age of the embryo on the day of freezing.
• A day 2 embryo is thawed and transferred three days after starting progesterone
• A day 3 embryo is thawed and transferred four days after starting progesterone
• A day 5 blastocyst is thawed and transferred six days after starting progesterone
• The progesterone and oestradiol valerate continue on the same dose until at least the time the pregnancy test is taken. If you become pregnant, you will continue to be prescribed both medications until you reach 12 weeks pregnant

Artificial cycle (without down regulation)

Having your embryos replaced during an artificial cycle means that the procedure does not depend on when you naturally ovulate to determine the day of transfer. This gives the clinic staff more control to schedule the embryo transfer at the best possible time.

For this procedure, you will be prescribed a medication known as oestradiol valerate from day one of your natural cycle. These tablets are used to thicken the lining of the womb (endometrium). After 10-12 days of taking this medication a scan is performed to check the endometrial thickness. You will continue to be scanned on alternate days until the endometrium measures 8mm or more. Once this thickness is achieved, you will be given progesterone in the form of pessaries (Cyclogest) or injections (Gestone) twice daily. We advise you to take the pessaries rectally at this time until after the embryo transfer when they can be used either rectally or vaginally.
The transfer takes place four to six days after starting to take the progesterone, depending on the age of the embryo on the day of freezing.
• A day 2 embryo is thawed and transferred three days after starting progesterone
• A day 3 embryo is thawed and transferred four days after starting progesterone
• A day 5 blastocyst is thawed and transferred six days after starting progesterone
• The progesterone and oestradiol valerate continue on the same dose until at least the time the pregnancy test is
taken. If you become pregnant, you will continue to be prescribed both medications until you reach 12 weeks pregnant

The embryo transfer

The embryo transfer itself is carried out in exactly the same way as the transfer following your fresh IVF cycle. It only takes a few minutes and you can go home immediately afterwards.

  • We carry out the embryo transfer under ultrasound scan guidance so you will need to have a full bladder
  • The embryologist will first discuss the grade of your embryos with you and whether one or two are to be transferred
  • Under recent HFEA guidelines we will only put three embryos back in exceptional circumstances in women over 40 years of age
  • Even when only two embryos are transferred there is significant risk of twins (up to 20%). Multiple pregnancies are associated with increased risk of premature delivery and cerebral palsy as well as most of the complications of pregnancy itself, such as diabetes and high blood pressure. In addition, once they are born, bringing up twins or triplets has financial, emotional and physical implications for the parents. By adopting a strict policy on numbers of embryos transferred we aim to keep multiple pregnancies to a minimum
  • The embryos are quite safe within the uterus and you can walk about, bathe, shower and carry on with your normal daily activities. However, it is best to avoid strenuous exercise until your abdomen feels less tender and back to normal. Sexual intercourse can be resumed whenever you feel like it
  • If you do not have a period in the two weeks following embryo transfer, a pregnancy test should be done. This can be a standard home pregnancy test or you may choose to come to the clinic for a blood test. If the test result is positive we can arrange for you to come in for an early pregnancy scan three weeks later (you will be seven weeks pregnant at this stage)
  • If the test result is negative you can stop the progesterone and oestradiol valerate and arrange a follow-up appointment with one of our consultants.
Before your treatment begins

Before you start your treatment cycle, please make sure that you have been given information about:

  • The limitations and possible outcomes of the proposed treatment
  • Possible side effects and risks of the treatment
  • The techniques involved
  • Costs
  • How it may affect your daily life
  • Counselling
  • The HFEA
  • Our duty to consider the welfare of any child resulting from treatment with us
Consent forms

Before starting your treatment cycle, we will ask you to read and sign a number of forms consenting to the thaw and transfer of your embryos. These will be discussed at your nurse consultation but if you have any queries please contact us at any time.

All consent forms must be completed and returned before you start treatment.

DisclaimerThe medical information provided here is as an educational resource only.

It is not intended to replace the advice of your GP or medical team and should not be used or relied upon for any diagnostic or treatment purposes.

The information has been prepared by Dr Carole Gilling-Smith, Consultant Gynaecologist and Medical Director of the Agora Gynaecology and Fertility Centre.

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Wednesday 8th of April (Postponed)

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