For patients with irregular cycles or ovulation disorders, and for patients who need to plan their therapy around time constraints, we can create an artificial menstrual cycle for FET. This involves treatment with an oral estrogen medication and is well established. Pregnancy rates are equivalent when compared to natural cycle FET.
With the advancement of assisted reproductive technologies, many more patients have embryos cryopreserved (frozen) after a fresh IVF stimulation. This is likely due to improved IVF stimulation techniques, improved laboratory environment for extended culture of embryos, development of new technologies for cryopreservation such as vitrification, and expansion of the use of preimplantation genetic testing (PGT). Within our clinic, 80-90% of cycles will have embryos cryopreserved. These cryopreserved embryos retain excellent viability despite the length of storage. In our laboratory, greater than 90% of cryopreserved embryos survive thawing.
The number of embryos transferred with a frozen embryo transfer is similar to that for a fresh embryo transfer and is based upon the guidelines established by the American Society for Reproductive Medicine.
When a patient desires to move forward with frozen embryo transfer, we may recommend a trial cycle if an endometrial biopsy or Endometrial Receptivity Assay needs to be performed. If you have been pregnant immediately before the FET cycle, we may recommend a repeat uterine cavity assessment with sonohysterogram (SHG) and/or a uterine measurement.
There are several different methods for preparation of the uterus to receive the embryo. The type of endometrial preparation does not appear to affect the live birth rate. However, several recent studies suggest that a natural cycle FET may be optimal to reduce the risk of pregnancy complications such as hypertensive disease of pregnancy, preterm birth, postpartum hemorrhage and placental issues.
A natural cycle FET (NC-FET) can still have multiple variations. In general, if a patient is having their own regular cycles, they can present for a cycle day 12 monitoring ultrasound. If the endometrial lining has an appropriate thickness and pattern, and there is a dominant follicle, a progesterone level will be checked to see if early ovulatory surge has occurred. If not, ovulation can be monitored with ovulation predictor kits or a trigger injection can be used to time the embryo transfer.
A programmed, or hormone therapy FET (HT-FET), may also have several variations. This is often recommended for patients with irregular menstrual cycles, for women who are post-menopausal, or for those who are using donor oocytes to create a fresh embryo for transfer. In general, a patient begins estradiol supplementation on day 3 of their natural menstrual cycle. A cycle day 12 monitoring ultrasound is used to assess the endometrial thickness and pattern. If this is adequate and there are no ovarian cysts, a progesterone level is checked to evaluate for ovulatory surge. If the progesterone is low, progesterone supplementation is initiated, and the embryo transfer is timed to the start of progesterone. The embryo transfer technique is similar to that of a fresh embryo transfer.
Hormone Replacement - FET Cycle Overview
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Step 1 - Estradiol Therapy
A dose of estrogen is usually administered for 14 days, although shorter or longer cycles may be used. Estradiol by mouth is the most common form of estrogen we use. This is a pill containing 2 mg of estradiol, the same hormone produced by the ovaries. We will have you take one pill twice, or three times a day for about 12 days.
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Step 2 – Ultrasound Evaluation
After approximately 12 days of estradiol treatment, you will be scheduled for a transvaginal ultrasound. Your physician will evaluate the development of the endometrial lining (where the embryo will implant in the uterus) to ensure it has reached an appropriate thickness and pattern. If the endometrial lining is not appropriately developed, you may be asked to increase your estradiol dosage and return for a repeat ultrasound. If the endometrial thickness and pattern are appropriate, a blood test to check your progesterone level will be checked. If it is low, you will be advised when to start progesterone supplementation.
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Step 3 – Progesterone Therapy
Progesterone therapy is necessary in hormone replacement FET cycles (unlike in a natural cycle FET) because the body is not making its own progesterone. Progesterone therapy will be administered as an intramuscular injection. Both estradiol and progesterone are continued through the embryo transfer and until the day of the pregnancy test (usually 10-12 days after embryo transfer).
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Step 4 - Embryo Transfer
Embryo transfer is performed on the third to fifth day of progesterone therapy (depending upon the stage of the embryo to be transferred). As with natural cycle FET, embryos are thawed on the morning of the scheduled frozen embryo transfer. The actual embryo transfer procedure itself is identical to the embryo transfer following IVF. Depending upon the physician’s protocol the embryo transfer may be accomplished under ultrasound guidance which will require the bladder to be full. A small plastic catheter is passed gently through the cervix into the uterus. The embryo is then deposited into the cavity along with a small amount of fluid. You will be allowed to leave after the procedure is complete. No anesthesia is required, so you can drive immediately after the embryo transfer if needed.
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Step 5 - Hormonal Studies - Pregnancy Test
We will usually perform a serum pregnancy test 10-12 days following the embryo transfer. If the test is positive, we may recommend additional blood tests and will recommend that you continue taking estradiol and progesterone for several additional weeks. If the pregnancy test is negative, estradiol and progesterone are discontinued, and a period will begin in a few days.
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Step 6 - Follow-up Consultation
If the pregnancy test is positive, we will perform a vaginal sonogram about three weeks later. At this point, we are usually able to identify the number of embryos and can often see a heartbeat. The risk of pregnancy loss is low after this developmental milestone. If the procedure is unsuccessful, you should schedule a consultation with your physician. We will review the procedure and discuss further treatment options.
UT Health Fertility Center doctors are also faculty at The University of Texas Health Science Center San Antonio School of Medicine. This allows us to remain one of the most cost-efficient fertility practices in the area. Our staff is happy to answer questions about referrals, itemized diagnostic and treatment costs and billing options. The UT Health Fertility Center participates in a variety of insurance plans. For your convenience, we accept VISA, MasterCard, and Discover.
Natural Cycle - FET Overview
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Step 1 - Monitoring of Follicle and Endometrial Development
Monitoring is performed by using transvaginal sonography during your natural menstrual cycle. Usually this appointment is scheduled on cycle day 12. You may have other ultrasounds as your dominant follicle nears maturity.
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Step 2 - Monitoring for LH Surge
As the growing follicle nears maturity, the level of the hormone LH in the blood and urine rises dramatically. This is known as the LH surge. For the purpose of frozen embryo transfer, we define the day of the LH surge as the day the urine LH test turns positive. It is important that the LH be monitored on a daily basis, as the frozen embryo transfer may be timed from the date of the LH surge.
Alternatively, a trigger injection may be used to induce an LH surge and ovulation to more precisely time the embryo transfer.
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Step 3 - Documentation of Ovulation
In addition to monitoring your LH, your physician may also confirm ovulation with ultrasound. If ovulation does not occur, as evidenced by failure of the dominant follicle to collapse on ultrasound, then the frozen embryo transfer may be canceled. Alternatively, hormonal supplementation may be provided during the remainder of the transfer cycle.
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Step 4 - Embryo Transfer
The day of the embryo transfer will depend upon the stage at which your embryos were frozen. Embryos frozen at a more advanced stage of development (blastocysts) will be transferred later than embryos frozen at an earlier stage of development.
Embryos are thawed on the morning of the scheduled frozen embryo transfer. The actual embryo transfer procedure itself is identical to the embryo transfer following IVF. Depending upon the physician’s protocol the embryo transfer may be accomplished under ultrasound guidance which will require the bladder to be full. A small plastic catheter is passed gently through the cervix into the uterus. The embryo is then deposited into the cavity along with a small amount of fluid. You will be allowed to leave after the procedure is complete. No anesthesia is required, so you can drive immediately after the embryo transfer if needed.
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Step 5 - Hormonal Supplements
Patients undergoing FET may not require hormonal supplementation (progesterone) when we document normal follicular development and ovulation. Unlike the initial IVF procedure during which the progesterone-producing granulosa cells are aspirated and removed, those cells remain functional within the corpus luteum during your FET cycle. Progesterone supplementation may be administered to patients with ovulatory dysfunction or luteal phase inadequacy. In these cases, progesterone injections or suppositories begin before the embryo transfer and continue until the pregnancy test is performed.
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Step 6 - Pregnancy Test
We will usually perform a serum pregnancy test 10-12 days following the embryo transfer. If the test is positive, we may recommend additional blood tests and will recommend that you continue taking progesterone for several additional weeks if you were prescribed this medication. If the pregnancy test is negative, progesterone is discontinued, and a period will begin in a few days.
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Step 7 - Follow-up Consultation
If the pregnancy test is positive, we will perform a vaginal sonogram about three weeks later. At this point, we are able to identify the number of embryos and can often see a heartbeat in the developing embryo. The risk of pregnancy loss is low after this developmental milestone. If the FET procedure is unsuccessful, you should schedule a consultation with your physician to review the procedure and discuss future treatment options.