FET – Frozen Embryo Transfer treatment
A frozen embryo transfer (FET) treatment cycle is where embryos which were frozen following IVF treatment are thawed and transferred (implanted) into the womb at a later date.
At BCRM we use the most advanced technique known as “vitrification” however, not every embryo created is suitable for freezing, our Embryologists work out which embryos meet the criteria and inform you of the possibility to freeze embryos. Success rates are much better when embryos are frozen at the blastocyst stage. Blastocysts are embryos that have grown to day 5-6 following fertilisation. We aim to freeze top quality blastocysts.
The embryos are usually frozen and stored at the blastocyst stage 5-6 days after egg collection. There are two types of FET treatment
1. Natural Cycle FET:
This is used in women who have regular cycles and ovulation, no drugs are used. Embryos are transferred after a positive ovulation test.
2. Programmed Medicated Cycle FET:
In a programmed FET you take medication, usually Estradiol tablets or patches to grow the lining of the womb until such a stage they are ready to receive embryos for implantation. Usually for 2 weeks and this is followed by progesterone pessaries to support implantation and development of the baby until 12 weeks of pregnancy.
What proportion of embryos survive the thawing process?
If we freeze top quality blastocysts, we find over 95% survive the thaw process ready for transfer. As such our aim is to do a Frozen Blastocyst Transfer (FBT)
What are the success rates with Frozen embryos?
In our hands the the success rates of FET treatment are similar to fresh IVF or ICSI treatment. In some cases the success rates are higher because the lining of the womb is not over-stimulated by high estrogen levels. The success rate also depends on the age of the woman when the embryos were frozen and not when transferred. It is for this reason we sometimes recommend a deferred IVF treatment cycle.
How long can we store embryos for?
Embryos can be store indefinitely with no deterioration over time. However, we do not routinely store embryos beyond 10 years.
What are the advantages of FET over Fresh IVF or ICSI treatment?
Less medication: no injections are required
No risk of OHSS: this is because the ovaries are not stimulated
Less stress: FET treatment is has a high chance of success because we only freeze top quality blastocysts and there is no ovarian stimulation, egg collection and therefore less visits to the clinic as well as less discomfort. This is particularly so in natural cycles where we have excellent success rates.
Less expensive: the cost of FET treatment is less than a third of a fresh treatment cycle of IVF or ICSI