Frozen Embryo Transfer: Natural Cycle
Natural Cycle Frozen Embryo Transfer: A Step-by-Step Guide
Each cycle of FET, like that of the other ART procedures, involves multiple steps, occurring at a specific time during a four-week period. An approximate timetable and overview are presented below. If you have been pregnant, or if it has been more than one year since your last embryo transfer, a repeat uterine measurement should be performed before FET. If you have never had an evaluation of the uterine cavity or if it has been longer than a year or if you have risk factors for uterine structural abnormalities, we will recommend a uterine cavity evaluation prior to FET, either with a saline infusion sonohystogram, office hysteroscopy or a hysterosalpingogram.
- Monitoring follicular development
- Monitoring for LH surge
- Documentation of ovulation
- Embryo transfer
- Hormonal supplements
- Pregnancy test
- Follow-up consultation
Step 1 - Monitoring of Follicle Development
Monitoring of follicle development is often performed during a FET cycle by using transvaginal sonography. To determine the day on which you should begin monitoring, subtract seventeen days from the length of your menstrual cycle. For example, if it is 30 days from the first day of one menstrual cycle to the first day of the next, you should have your first ultrasound on approximately cycle day 13 (30-17=13). You will have other ultrasounds as your dominant follicle nears maturity. These ultrasounds will continue until we have documented ovulation.
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 will be timed from the date of the LH surge. The timing 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.
Step 3 - Documentation of Ovulation
In addition to monitoring your LH, your physician may also confirm ovulation with ultrasonography through the time of ovulation. 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. Depending upon the individual physician’s protocol you may also be treated with oral medications such as methylprednisolone and doxycycline prior to the transfer.
Step 4 - Embryo Transfer
Embryos are thawed on the morning of the scheduled frozen embryo transfer. In our laboratory, approximately 60-70 percent of embryos survive cryopreservation and thawing. We usually transfer 1-2 embryos during each FET cycle. However, this number is flexible, and your physician will discuss this issue with you. Excellent FET pregnancy rates occur in most cases with the transfer of one to two embryos, which also minimizes the risk of multiples. The transfer of more embryos may increase the likelihood of a multiple pregnancy, which increases the pregnancy risks for the woman and the fetuses.
The actual embryo transfer itself is identical to the embryo transfer following in vitro fertilization-embryo transfer. 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. After waiting 1-2 minutes to allow any mild cramping to resolve, the embryos are deposited in the cavity along with a very small amount of fluid. No anesthesia is required for the embryo transfer. You will be discharged after resting for 20 minutes.
Step 5 - Hormonal Supplements
Patients undergoing FET may not require hormonal supplementation when we document normal follicular development and ovulation. Unlike the initial IVF-ET procedure during which the progesterone-producing granulosa cells are aspirated, 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.
Step 6 - Pregnancy Test
We will usually perform a serum pregnancy test 12-14 days following the embryo transfer. If the test is positive, we may measure the serum progesterone level and recommend that you continue taking progesterone for several additional weeks. If the pregnancy test is negative, progesterone is discontinued and a period begins in a few days.
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.