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Transfer of Frozen Embryos

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Introduction

Many of you will be aware that it has been possible for some time to freeze (cryopreserve) embryos that are not used during your first treatment attempt. These embryos can be thawed at a later date and transferred back to the womb after suitable preparation of the lining of the womb. Transfer of these frozen/thawed embryos is not as successful at establishing pregnancies as the transfer of embryos which have not been frozen, but they do represent a second or even third chance to achieve a pregnancy without having to undergo the full course of injections to stimulate the ovaries and the egg recovery procedure.

If there are a sufficient number of fertilised eggs from your fresh cycle it is usually possible to freeze the spare embryos for future use. There are three times at which the embryos could be frozen:

  • At 16 hours of age before the fertilised egg has actually divided (pronucleate stage)
  • When the embryos actually divide into between 2 to 4 cells (early cleavage stage).
  • At five days after fertilisation (blastocysts), only a small amount of embryos survive to this stage.

Egg Freezing

Most embryos are nowadays frozen at the early cleavage stage. In this situation all embryos are left in culture and the best 2 embryos are transferred into you. If there are 2 or more Grade 1 embryos remaining following the transfer, these will be cryopreserved for future use.

Pronucleate stage freezing mainly occurs if ovarian hyperstimulation occurs and it is unwise to transfer fresh embryos into your womb.

At present approximately 31% of women have sufficient embryos to allow freezing.

If you request it we can arrange for transfer of the frozen embryos fairly soon after your initial “fresh” treatment. There is no evidence that embryos are actually affected by the length of time they are frozen. We understand that any damage is caused during the course of cooling the embryos to freezing point and warming to body temperature.

Thus it has been known for a couple to achieve two pregnancies from one cycle of treatment and for a couple to have their “twins” two, three or four years apart.

Following your initial attempt where the fresh embryos are transferred you will be asked to attend the Infertility Clinic in Halifax, to discuss further options. In general we prefer it if you have all your frozen embryos transferred prior to contemplating any further fresh IVF cycles.

Transferring of Embryos

For the transfer of frozen embryos to be successful, the embryos must be put back into the womb when the womb lining (endometrium) is ready to receive the embryos. There are two ways of achieving this, either in a natural cycle or during an artificial cycle.

Natural cycle embryo replacement is relatively simple and requires monitoring.  Your endometrial development, measured by ultrasound scan, combined with ovulation predictor kits (which tests hormones released into your urine), tells us when you are about to release an egg. With a combination of these tests we can tell when the lining of the womb is ready to receive the embryo.

Replacing the embryos in fresh cycles, however, is not as successful as replacing the embryos in an artificial cycle. We, therefore, usually advise frozen embryo replacements during an artificial cycle in which your natural hormones are suppressed with an injection administered on the 21st day of your cycle. This injection lasts approximately one month. Once your own hormones are suppressed we ask you to commence oestrogen tablets to make the womb lining thicken, and later in the cycle progesterone (Cyclogest) pessaries or gestone injections to make the womb lining ready to receive the embryos.

FET Cycle

How Do We Start?

How Do We Start?

We do not have a waiting list for frozen embryo transfer cycles. When you are ready for your treatment you must phone Sue McCabe the Business Manager on 01422 224257 within a week of commencing your menstrual cycle. We will ask you and your husband/partner to attend on the 21st day of your cycle, to sign consent forms and to have the injection administered following a scan. This will suppress your cycle. If your G.P. is prescribing your medication, you must ensure to bring your medication with you. If your G.P. is not prescribing your medication, Mr DeBono’s secretary will send you a hospital prescription after you have phoned her or with your confirmation letter. Please ensure you bring your medication to your appointment.

You should expect to have a further period about 7 days after the injection has been administered. You will be asked to come back for a scan 14 days after your injection to check that your ovaries are inactive, and to check that the lining of the womb is thin. Occasionally we find that you will not have had a period and the womb lining is still thick, in which case we will see you again a week later.

The Preparation

The Preparation

If all is well you will start you oestrogen tablets (usually Oestradiol).  You will be advised of the dosage required by the nursing staff at that time. You will return for a scan 8-10 days after the commencement of the tablet treatment. The scan will indicate whether the womb lining is thickening sufficiently. Depending on these results, we may have to adjust the amount of tablets or even start you on skin patches to ensure the correct development of the womb lining.

It may therefore be necessary to arrange further scans and blood tests as necessary until the womb lining is ready to receive the embryos.

Once the womb lining is at least 8-10 mm thick, you will be asked to start inserting either 2 progesterone (Cyclogest 400mgm) pessaries every night or a daily intra muscular injection of Gestone. You should continue with the oestrogen tablets and after 3 days of pessaries/injections have been started you will attend the Clarendon Wing, Leeds General Infirmary or St James’ University Hospital in Leeds, Care Manchester for your embryo transfer.

You will have discussed and decided on the appropriate amount of embryos to thaw at your first visit with the nursing staff. The embryologists will then select out the best embryos that have survived the freezing and thawing process and transfer the best 1 or 2 embryos, depending on your circumstances.

The Embryo Transfer and After

The Embryo Transfer and After

The transfer itself is identical to previous embryo transfers you will have had. You should continue your oestrogen tablets and progesterone pessaries/injections on exactly the same dose as before until the results of your pregnancy test come through. You will be asked to return to Halifax 12 days following your embryo transfer for a pregnancy blood test. You will be able to find out the result by contacting the Assisted Conception Unit on 01422-224478 after 2.00pm that same day.

If the test is negative, you will be advised to discontinue all your tablets and pessaries/injections, and you will be given an appointment to see Mr DeBono in the clinic 2 to 4 weeks later. If the result is positive you must continue on your medication for a further 10 weeks. This is to provide the pregnancy with the support it needs until it becomes self-sufficient. We will also organise further blood tests/scans to check on the progress of your pregnancy.