Frozen Embryo Transfer (FET)
A frozen embryo transfer or FET, takes an embryo cryopreserved from a previous IVF cycle or a donor embryo, and thaws it before transferring it into a woman’s uterus. The advancements in cryopreservation techniques and use of vitrification have allowed for increased success rates when using frozen embryos. Woman who have a good ovarian reserve and are under 35 often times have embryos that can be frozen. After a woman turns 35, her chance of having embryos left for cryopreservation decrease dramatically. Once an embryo has been cryopreserved it can be stored indefinitely. Woman can use the embryos for future children knowing that the age at which they frozen the embryos are the age the embryos will remain.
A frozen embryo transfer can occur:
- After a successful fresh transfer when a woman is trying to conceive her next child years later
- After an unsuccessful fresh transfer, anywhere from months to years later when the woman is ready to try again
- When the couple decides to undergo genetic testing on their embryos, which results in the need for cryopreservation of the tested embryos
- When medically a fresh transfer is not in the best interest of the patient (ex: OHSS, elevated progesterone levels)
The success rates of fresh versus frozen transfers are comparable. The type of transfer chosen will be based on a number of factors specific to your situation; which the physician will discuss with you. In some cases, a frozen embryo transfer can have better success rates.
- Less Medication – During an FET cycle less medication is used as we are not stimulating the ovaries. Progesterone and estrogen are used to prepare the uterine lining for implantation. Progesterone and estrogen are continued through week 10 of gestation to continue to maintain the uterine lining at which time the placenta is able to take over.
- Progesterone Levels – During ovarian stimulation in an IVF cycle elevated progesterone levels can cause the uterine lining to be less receptive to implantation. If progesterone levels reach a certain threshold the physician may recommend that the planned fresh transfer be cancelled. The embryos would then be cryopreserved for a future FET.
- Less Stress – FET cycles are more predictable. Patients have a choice of transfer dates months in advance which will then determine the date their cycle will be initiated. Since the embryo is already created, the number of eggs, how many fertilized, how many made it to day 5 are already known.
- Less Costly – Due to less medications, less monitoring, and a less invasive procedure frozen embryo transfers cost substantially less than a fresh transfer.
To prepare for an FET:
- Patients take estrogen injections to thicken the uterine lining for 15 to 22 days prior to the transfer date
- Based on the thickness of the lining, progesterone is administered around day 5 to 6 to prepare the uterus for the thawed embryo
- On the day of the transfer the laboratory thaws the embryo(s) for the transfer
- Using a soft, ultra-thin catheter, under ultrasound guidance, an embryo is transferred into the uterus. The procedure takes approximately 2 minutes and no anesthesia is required. Discomfort is similar to that of a pap smear.
- Patients then wait two weeks to take a pregnancy to see if implantation has occurred.
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