Referral & Treatments

Frozen embryo transfer

It has been possible for some time to freeze (cryopreserve) embryos which 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.

The embryologists assess whether fertilisation has taken place on the day after egg-collection. At this stage the embryo is still one cell and has not yet divided and its quality can therefore not be assessed. On the following day, that is the day of embryo transfer, we would expect the embryos to have divided into 2 or maybe 4 cells. This stage is called early cleavage (EC). At this stage the embryos can be assessed depending on the regularity of the shape of the cells and whether the cells have fragmented to any degree. The degree of fragmentation of the cells enables the embryologists to obtain an impression as to their quality and only embryos in which there is minimal fragmentation are suitable for freezing.

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 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 of four years apart.

Instructions for Frozen Embryo Transfer

For the transfer of frozen embryos to be successful the embryos must be put back into the womb when the lining of the womb (endometrium) is ready to receive 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 of the development of the endometrium by ultrasound scans combined with ovulation prediction kits (which test the hormones released into your urine), which tell us when you are about to ovulate. Using a combination of these tests we can work out when the endometrium is ready to receive the embryos.

The alternative is to use an artificial cycle in which the natural hormones are suppressed with the injection of Prostap or Zoladex, administered on day 21 of your cycle. This injection works for a month and is a longer acting form of the nasal spray or daily injections that you would have received for your IVF treatment. Once your hormones are suppressed we ask you to commence oestrogen tablets to thicken the endometrium. When the endometrium is of an appropriate depth you are then given progesterone support to make the endometrium receptive to the embryos.

The success rates of both techniques are similar although we prefer to use the artificial cycle for logistic reasons.