What is Frozen Embryo Transfer?
Frozen Embryo Transfer (FET) is an IVF treatment, in which cryopreserved embryos are thawed and transferred to a woman’s uterus. Often patients ask to freeze and store any extra embryos that are not used in their first cycle, at the event of a failed cycle or for the desire of another child. Women may choose this option for fertility preservation or because their hormonal profile and/or uterine lining is not optimal during a fresh IVF cycle. A patient preparing for an FET has blood testing and ultrasound scans that enable her physician to identify the appropriate point in the patient’s cycle to transfer the embryo(s). Some FET patients may also take hormone medication to prepare for the transfer.
FET with Hormonal Support
Doctor may recommend FET with hormonal support for patients with irregular cycles and/or have to plan around time constraints. FET with hormonal support involves administering hormones such as estrogen and progesterone to suppress or control ovulation as well as ensure that the patient’s endometrium (uterine lining) is prepared for the transfer. Embryo transfer takes place on the third or fifth day of progesterone support.
FET Natural Cycle
FET natural cycles, on the other hand, do not involve medications that control ovulation, instead it is based on when ovulation naturally occurs. The patient’s doctor closely monitors her menstrual cycle through blood tests and ultrasound to identify the optimal day for embryo transfer. The frozen embryos are thawed and are transferred to the uterus.
Until the flash freezing process, known as vitrification was introduced a decade ago, frozen embryos had a very low implantation and live birth rate. There were various reasons for the low numbers. One of the primary issues was the freezing process itself. The slow freezing method enabled ice crystals to form within the embryo, which damaged it to the point at which they were not longer viable. Fortunately with the development vitrification, over 90% of the frozen embryos survive thawing and are the same quality as fresh embryos. Vitrification is the process of freezing eggs and embryos with extremely rapid cooling, which is too fast for crystals to form. The improvements in the freezing process and in the selection of embryos process, frozen embryos are now frequently used and proven to result in successful pregnancies.