Embryo freezing (cryopreservation) as part of IVF
It is very common for more eggs to be produced during an IVF cycle than can be used or are needed for one cycle. Extra embryos which are of suitable quality can be frozen and stored in liquid nitrogen (cryopreserved) for future use. The possibility of this is discussed before treatment takes place.
Pregnancy rates using frozen embryos
Freezing of embryos is a delicate and difficult procedure and not all embryos survive the procedure. Freezing can also cause subtle damage to the embryo. The pregnancy rate after frozen embryo transfer is therefore usually lower than that of fresh embryo transfers.
Frozen embryo storage
Under the Human Fertilisation and Embryology Act freezing of human embryos can only take place at a centre that is licensed for the procedure. The Act also states that the maximum storage period for frozen embryos is five years, although this can be extended in special circumstances. More information about the Human Fertilisation and Embryology Act can be found on the HFEA website
Frozen embryo transfer
Thawing and transfer of the frozen embryo (frozen embryo transfer cycle) may occur either in a spontaneous (natural) cycle or a controlled cycle using drugs to create conditions ideal for embryo implantation in the uterus. In a spontaneous cycle the patient undergoes ultrasound scanning until a follicle with a diameter of 14mm is produced. A urine ‘ovulation prediction’ test is used daily and the patient should inform the unit when the test is positive.
The actual process of transfer is identical to that used in a fresh IVF procedure with a catheter being used to insert the embryos into the womb. More information about IVF can be found on the IVF Treatment page.