Embryos may be transferred anytime between day 1 through day 5 after the retrieval of the eggs depending on individuals’ condition. Embryos can be either “fresh” from fertilized egg cells of the same menstrual cycle, or “frozen”, that is they have been generated in a preceding cycle and undergone embryo cryopreservation, and are thawed just prior to the transfer, which is then termed “frozen embryo transfer” (FET).
The endometrium is believed to not be optimally prepared for implantation following ovarian hyperstimulation, and therefore frozen embryo transfer avails for a separate cycle to focus on optimizing the chances of successful implantation. The outcome from using cryopreserved embryos has uniformly been positive with no increase in birth defects or development abnormalities.
The evidence supports FET in women more than 35 years of age. When taken together from large observational studies and RCTs, is growing, not only in terms of achieving higher pregnancy rates but, more importantly, also in terms of lower maternal and infant morbidity and mortality. The process of embryo transfer is the same for both fresh and frozen cycle. The different is the uterine preparation protocol. The fresh cycle, embryo will be transferred on day 2-5 after egg pick up. It is a simple non-invasive procedure anesthesia is often not necessary. An ultrasound may be used to help guide the physician as he transfers the embryos. A predetermined number of embryos are loaded into a fine transfer catheter that passes through the vagina and cervix, into the uterus. Following this procedure, the patient usually remains in a recovery room resting on her back and is discharged 4-6 hours after the procedure. Progesterone is often the main medication that a woman will continue to take after the embryo transfer. Taking supplemental progesterone will not only help increase the chances of pregnancy, but progesterone is also vital to sustain a pregnancy.
During a normal menstrual cycle, estrogen is produced by the developing follicle. This estrogen acts on the uterus to thicken and mature the uterine lining. This protocol depends entire on the women’s body, with no artificial hormone given. A transvaginal ultrasound is performed to determine the thickness of the uterine lining and a blood test is performed to look at the level of estrogen in the blood and to determine the transfer date.
During this estrogen is given, the woman will come to the office periodically to be monitored. On occasion, if the lining is not thickening as it should, the dose or type of estrogen must be increased or prolonged.