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Frozen Embryo Transfer - FET

What is Frozen Embryo Transfer (FET)?

Arizona Center for Fertility Studies has been cryopreserving, thawing and transferring embryos for a number of years with current success rates of 80+%, depending on the age of the woman when the embryos were frozen. FET, or frozen embryo transfer, is a term used when extra embryos from an In-Vitro Fertilization (IVF) cycle are cryopreserved and later thawed and transferred into the prepared uterus.

Frozen Embryo Transfer (FET) Procedure

Prior to the transfer, all other causes of infertility should be evaluated and appropriately treated, as to not overlook something, "possibly simple", that can interfere with the FET being successful. Just because a woman was successful on her last attempt, does not mean she will be successful on her next attempt. Things can change between pregnancies or over time, and a common mistake is to assume that things "are status quo". Blood tests need to be updated if they are a year or older, Hysterosalpingogram (HSG) needs to be done to document that the fallopian tubes are still open and Arizona Center for Fertility Studies requires a Sonohysterogram (SHG) within 3 months of a transfer to rule-out any uterine pathology, like polyps or fibroids.

Once all the appropriate testing has been done, the Frozen Embryo Transfer (FET) cycle can start. Both the older literature as well as the new literature has shown that a prepared cycle with estrogen and progesterone results in higher pregnancy rates and live births than transferring on a woman's natural cycle. This may be due to several reasons. In the older reproductive woman, her "older eggs" may not be able to optimally prepare the cycle; and in a younger woman, it is thought that by eliminating all signals from the brain to the ovary, implantation rates and subsequent pregnancy rates are higher, suggesting that "these normal signals" may somehow interrupt the optimum uterine preparation when doing a frozen embryo transfer. If a woman has to do a natural cycle transfer, usually from persistent simple cyst development from Lupron or "an allergy" or "problems" with taking progesterone injections or gel, pregnancy rates are still good. If a natural cycle is done, then follicular growth of a single follicle is followed with frequent ultrasounds and when the follicle reaches 18 mm in size, ovulation is triggered with 10,000 IU of hCG, estrogen is checked to confirm that the egg follicle is "mature"; the embryos are thawed and embryo transfer is done 3-5 days later corresponding to the day the embryos were frozen. Sometimes these cycles are supplemented with oral estrogen and low dose natural oral progesterone. Since natural cycles are difficult to control, it might mean working on Saturday or Sunday; but that's okay.

In doing Frozen Embryo Transfer (FET), in order to "prepare" the cycle, all the signals from the brain to the ovary are blocked with a drug called Lupron, which temporarily puts the woman in menopause. Don't worry, it is always reversible and the symptoms are only for a few weeks. Lupron is started on day 1 of a bright red bleed, after an ultrasound is done to rule-out any simple ovarian cysts. Lupron can actually stimulate these simple cysts before suppressing the cycle. After 30 days on Lupron, another ultrasound is done to confirm that there are no ovarian cysts, and the woman is started on oral estrogen (E2), or Estrace, to start to build-up and prepare the uterine lining, or endometrium, for implantation. After 18 days of Estrace, Lupron is stopped, and either progesterone (P4) injections or progesterone vaginal gel (Crinone) is started for the final preparation and maturation of the uterine lining so that implantation can occur (Should I use progesterone after IUI or In-Vitro Fertilization (IVF)?). Oral progesterone does not work because you cannot give a high enough dose to support the lining. Prior to the start of progesterone, the final ultrasound is done to measure the "thickness" of the uterine lining to make sure that estrogen prepared it properly for implantation. The lining should measure 9 mm or greater to be prepared for implantation. Progesterone is continued for 3-5 days before the embryos are thawed. The actual number of days on progesterone is based on the age in days that the embryos were frozen. In other words, if the embryos were frozen on day 3 post fertilization as 8-cells then they are transferred on the third day of progesterone. If they were frozen as blastocysts, or on day 5, then they are transferred on the 5th day of progesterone. Uterine embryo transfer (UET) of the appropriate number of embryos is carried out based on ASRM guidelines (In-Vitro Fertilization (IVF)).After the embryo transfer, the woman is continued on estrace and progesterone. A blood pregnancy test is done 9-11 days later, depending if was a day 3 or day 5 transfer. If the test is positive, the estrogen (E2) and progesterone (P4) are continued until 12 weeks of pregnancy. At that point in the pregnancy, the placenta is fully functional and is making all the hormones that the ongoing pregnancy needs, and the the (E2) and (P4) can be stopped. An initial ultrasound is done at 6 weeks and then every 1-2 weeks until 12-14 weeks when the woman is referred to an obstetrician for continuing OB care.

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