What is Frozen Embryo Transfer (FET)
A frozen embryo transfer is when unused embryos are saved for later use. These are frozen and will require to be thawed before deposition in the womb. Frozen embryo transfer cycles use embryos that had been previously created, sometimes even years earlier, and then will be placed into the uterus. The success rates evidenced in frozen embryo transfers are evidenced to be higher than fresh embryo transfers.
Frozen embryo transfers have been rather common with the advent of technology that provides better freezing and preservation facilities. There are several advantages for patients to seek frozen embryo transfers one of the most common ones is that the patient will always have a bank of embryos that can be used in case of a failure or any contingency.
If a patient doesn’t get pregnant, has a pregnancy loss, or has had a baby but would like another, they can use the extra embryos that have been previously created. Also, patients seeking genetic testing of the embryos will require to freeze the embryos while waiting for test results. And finally, if there is are issues with the endometrium, and require a complete evaluation – because of the presence of a polyp or a thin endometrium, the transfer may be cancelled until the uterus can be evaluated completely – during which time the embryo will be required to be frozen.
Frozen Embryo Transfer and Desynchronization in IVF
In the normal course of a menstrual cycle, the estrogen levels peak right before ovulation which triggers the release of the egg and the production of progesterone. The endometrial lining of the uterus then starts developing which then allows for the fertilized egg to be implanted. Thus, in the natural course of things, progesterone production in the body is consistent with ovulation and the lining of the uterus develops per the need to nurture the fertilized egg.
This progressive synchronization between the progesterone response and the development of the endometrial lining provides the best environment for implantation of the egg. However, during the course of an IVF cycle, the estrogen peaks are higher than normal, and it is the higher estrogen peaks that actually trigger progesterone production. There is a chance that the estrogen peaks may trigger an early progesterone response and the endometrial lining develops too quickly than required.
This desynchronization of the development of the endometrial lining and the implantation of the embryo is likely to cause unsuccessful implantation. Thus, patients may be placed on medications that regulate progesterone production. However, not all cases of such regulated progesterone production would be successful, and some patients may still suffer from such desynchronization despite best efforts.