Frozen embryo transfer (FET) is defined as the use of frozen (cryo-preserved) embryos for In-Vitro Fertilization (IVF). Frozen embryos which were created in a previous stimulated IVF cycle are thawed and transferred in a current IVF cycle. FET is possible only if additional (or spare) embryo(s) of the couple seeking treatment are available in a frozen and preserved condition from the previous IVF cycle for future attempts. Use of frozen embryos allows embryo transfer when the endometrial lining is mature to adequately nurture the fertilized eggs. Timing is most important issue in Assisted Reproductive Technology.
It is best to transfer one embryo per cycle since transferring two or more may increase the chance of a multiple pregnancy and associated complications.
FET has impacted IVF in several ways in improving the various outcomes. It is indicated in the following conditions:
i. Unsuccessful initial IVF cycle
ii. Prevention of ovarian hyper-stimulation syndrome (OHSS) which is a potentially serious complication of IVF. It is advisable to freeze all the embryos and use them after thawing in a subsequent month.
iii. Premature rise in progesterone level
iv. Embryo biopsy for pre-implantation genetic screening or diagnosis (PGD).
v. Slow growing embryos
vi. Embryos cryo-preserved for Fertility Preservation in cases of cancers
A large number of reports cite better pregnancy rates with FET. This is possibly because the uterine lining is more “physiological and receptive and also that the transfer date can be postponed if the thickness of the uterine lining is not adequate. We at your best infertility center in Chandigarh routinely use frozen embryos for almost all cases for this very reason. As per standard practice, we use vitrification and culturing of embryo for 5-6 days up to blastocyst stage before transfer. This has further improved our results.
Besides better success rates, there are a few reports that mention the 10% greater likelihood of a live birth following IVF-FET than a fresh one. It is also reported that FET babies have better birth weight, less incidence of prematurity and intrauterine growth retardation.