Frozen embryo transfers contribute an increasing percentage of births from assisted reproductive technologies such as IVF. Currently, about 30% of frozen embryo transfers result in a live birth. For optimal success, the endometrium (uterine lining) needs to be precisely synchronized with the developmental stage of the thawed embryos. This synchronization can be achieved in one of the two ways described below. The likelihood of successful outcome is comparable with both strategies but more cancellations occur in natural cycles because ovulation often does not occur as expected.
Preliminary Testing Before FET
A follow-up visit to discuss any clinical changes, to select the synchronization strategy and to outline the details of the treatment plan is worthwhile. Since the chance of pregnancy depends upon the viability of the embryos, receptivity of the uterus and the ease of the embryo transfer procedure, these major areas are scrutinized closely. Unfortunately, embryo viability cannot be definitively evaluated until the embryos are thawed.
Uterine receptivity depends upon the structural integrity and endometrial thickness which are both evaluated by a saline infusion sono-hysterogram (SIS). SIS is typically performed in the cycle before FET but it can be done in the actual treatment cycle as well. During SIS sterile saline is introduced into the cavity to better outline small polyps or sub-mucous fibroids which might interfere with embryo implantation. If endometrial polyps or fibroids are found then hysteroscopy can readily remove them.
Normal cavity on SIS test
Embryo transfer procedure is key to successful outcome of all A.R.T.s. In patients with a narrow or tortuous cervical canal the passage of the transfer catheter is often difficult. In such cases a trial transfer is done with a full bladder and ultrasound guidance in the Transfer Room at Alta Bates Medical Center exactly as the actual FET is performed. In some cases with a very narrow cervical canal, laminaria are placed in the cervix to open the canal in preparation for the upcoming SIS and FET.
“Artificial Ideal Cycle” Protocols
This protocol involves sequential administration of natural estrogen and progesterone. In such cycles ovulation does not occur and the resulting pregnancy needs to be supported until the placenta matures at 10-12 weeks. In addition to its reliability and flexibility, the major advantage of this approach is that the day of transfer is chosen with ample notice to accommodate your and our busy schedules.
Natural estradiol is started on the second day of full menstrual flow. The most common preparation is injectable estradiol valerate (DelEstrogen 10 mg/mL). If you have a more concentrated form of DelEstrogen (20 mg/mL) please make sure to tell the Nurse Coordinators so the volume of your injection can be adjusted accordingly. Estradiol valerate is given as IM injections twice per week for 2-4 weeks. In patients known to require high dose, estradiol in the form of tablets (Estrace 2 mg) is added vaginally. In some cases estradiol can also be given orally or as patches.
After 7-14 days on estradiol a vaginal ultrasound is done to measure endometrial thickness and the schedule of medications is modified as needed. In some cases a second ultrasound is required. Blood is drawn to confirm that no ovulation has occurred. Once the endometrium has reached its full development, the FET is scheduled and the final progesterone schedule is provided.
Progesterone is usually given in the form of micronized vaginal capsules and IM injections of progesterone-in-oil (50 mg/mL). Please note that micronized progesterone capsules are made by compounding pharmacies and may vary in their absorption. If you get Prometrium, which have a thicker capsule, you should soften moisten them in warm water before insertion. Endometrin tablets and Crinone gel are other forms of vaginal progesterone used in our program. Our Nurse Coordinators can tell you which pharmacies are reliable sources of micronized progesterone capsules.
Natural Cycle FET
In select cases, synchronization can be achieved during the woman’s spontaneous cycle provided that her ovarian function is normal. One of the advantages of natural cycles FET is that few if any injections are required but the timing of transfer is often unpredictable. Call our office on the first business day after the onset of full menstrual flow to schedule a baseline ultrasound. About 2-3 days before expected ovulation another ultrasound is done to confirm presence of a pre-ovulatory follicle and normal endometrial development.
At the baseline ultrasound appointment you will be told when to start testing for an LH surge at home. Ovulation prediction (LH-detection) kits give 24-36 hour notice of ovulation and are sold without a prescription. A test is positive when your dot is close to, equal to or darker than the reference dot. Computerized ovulation predictors can also be used for timing of FET.
Setting the Day of FET
In our program embryos are frozen at 1, 2, 3, 5 or 6 days after egg retrieval, and some patients have embryos frozen at more than one stage. The exact timing of transfer takes into account the stage at which the embryos were frozen as well as endometrial development on one of the above protocols.
Frozen Embryo Transfer Procedure
After the embryos have been thawed, and found to be suitable for transfer, a small tube is gently passed through the cervix into the uterus and the embryos are deposited in the uterine cavity. The transfer requires no anesthesia. If at all possible, we would like your partner to be present. We use an abdominal ultrasound to confirm that the catheter is within the uterine cavity. Therefore it is best if you drink extra fluid 1-2 hours and stop voiding about 1 hour before the transfer. In the usual position for a pelvic examination, a tiny catheter containing minute amount of fluid with the embryos is gently inserted into the uterus and the fluid is deposited. You then rest for 5-10 minutes before discharge. After the transfer you might notice light spotting for a couple of days.
Following FET we advise patients to refrain from orgasm and ejaculation of semen into the vagina for 5 days in order to minimize uterine contractions which could expel the embryos through the cervix or up into the fallopian tubes and thus prevent normal implantation within the uterine cavity.
Transfer room is adjacent to the laboratory