Who can benefit from FET?
FET can be of huge benefit to couples undergoing IVF, as it means that if their first cycle is unsuccessful they’re able to try again much more easily. Having a frozen embryo eliminates the need for egg or sperm collection and can reduce the amount of hormone stimulants required. It also avoids the risks of Ovarian Hyper-stimulation Syndrome (OHSS). What’s more, using frozen embryos can significantly cut the cost of a treatment cycle (although there will be some costs involved in storage).
FET is also of huge benefit to women who are facing an infertile future as a result of surgery, chemotherapy, or disease. As long as a healthy uterus remains, FET could still allow a successful pregnancy.
Occasionally, FET is recommended for women undergoing IVF if there is a high risk of severe OHSS, as the hormones produced in pregnancy can make this worse. In this case, the embryos are frozen to allow the woman to recover from the stimulation phrase before they’re implanted.
The FET Process
Embryos can be frozen at several stages of development:
- Pronuclear Stage – embryos can be frozen immediately after fertilisation, giving them the highest chance of survival. However, as the embryos have not developed at this stage, it is hard to assess their viability.
- Cleavage stage – embryos can be frozen at the first division stage, two or three days after fertilisation, allowing for limited assessment.
- Blastocyst stage – embryos are most often frozen at the 8+ cell stage, the same point at which they would normally be transferred to the uterus - when the healthiest embryos can be easily identified.
Embryos are usually frozen for a maximum of five years, although this can be extended to ten. In the case of cancer patients, this limit may be extended further.
In order to create the ideal conditions for successful conception, the woman’s cycle is usually chemically controlled. This ensures the uterus has thickened properly and is ready to accept the embryo on the appointed day. A series of hormone treatments is prescribed, starting with oestrogen to thicken the lining of the uterus, followed by progesterone to mature the uterus ready for implantation.
Because the embryos can be thawed when needed the process is far more flexible than standard IVF, which is governed by follicle growth, and so puts less pressure on the woman involved.
It is possible to undergo frozen embryo transfer as part of a normal menstrual cycle, but the natural variation of this can create planning problems for both the patient and the clinic.
As a rule, no more than two embryos are implanted, however, in the case of women over forty, a third embryo may be considered.