Previously frozen embryos may be transferred during a woman's natural cycle or in a controlled (artificial) cycle, depending on a number of factors:
Controlled cycle transfer.
In a controlled cycle, hormone medications are given to prepare the uterus for transfer. This method is recommended for patients who have irregular cycles. Because the controlled cycle can be precisely timed, it is also advised for those who are on a set travel schedule. The medications commonly used for a controlled cycle are estrogen (either in an injectable or oral form) and progesterone (in either an injectable or vaginal form).
Natural cycle transfer.
Patients who have a regular menstrual cycle may have the option of using their natural cycle for transfer of frozen-thawed embryos. In this case, there is no need for hormone treatment, as the body's natural cycle will prepare the uterus for pregnancy. In cases where natural cycle transfer is possible, this option allows for less medication and monitoring and thus is often relatively affordable for patients. We typically will monitor the natural cycle using home urinary ovulation predictor kits as well as ultrasounds. When the kit changes and/or a nice pre-ovulatory follicle is seen on ultrasound, we administer a single injection of Ovidrel (recombinant subcutaneous hCG) and the patient starts progesterone vaginal suppositories a couple of days later. The embryo transfer will occur 5-7 days after ovulation/hCG injection, depending on whether the embryos are frozen at a Day 3 or Day 5 stage.
For the transfer procedure itself, the embryo is thawed at room temperature, and then warmed to body temperature (37° C). As with a fresh embryo transfer, embryos are placed inside a special catheter (a very thin tube), which is guided through the cervix and into the uterus. Embryos are gently injected into the uterus and the catheter is removed. This procedure requires no anesthesia, and is done in a position similar to a pelvic examination for a Pap smear. After transfer, the woman rests for 15 minutes and then is able to go home, where a day of rest or very gentle daily activity is recommended.
