Facts about Frozen-Thawed Embryo Transfer

The transfer of embryos to the uterus after having been previously cryopreserved and thawed is referred to as Frozen-Thawed Embryo Transfer. This important procedure is useful for the management of infertility, with generally positive outcomes comparable to fresh embryo transfers.

Women who have a high risk for ovarian hyperstimulation syndrome (OHSS), or those who require a quarantine period for embryos or even unfertilized oocytes are not good candidates for fresh embryo transfer. Thus, Frozen-Thawed Embryo Transfer offers a viable solution for these patients and another chance at getting pregnant.

Before beginning the process, initial consultation, screening, and other tests must be conducted. The process begins with the administration of gonadotropin-releasing hormone or follicle-stimulating hormone to stimulate her ovaries. Around the time of ovulation, oocyte retrieval is carried out. This can be done with or without ultrasound guidance. The oocytes can then be fertilized using in-vitro fertilization.

Three days after fertilization, the fertilized egg has reached the embryonic stage of development. Either slow programmable freezing or vitrification can be used as a cryopreservation protocol. Prior to the transfer procedure, the patient is given estrogen preparations followed by a combination of estrogen and progesterone to develop a uterine lining that is favorable for implantation. When the patient has reached the appropriate point in her menstrual cycle, her uterus is ready for implantation.

Embryos are transferred when they are comprised of eight cells. However, they may be transferred farther along in their development as blastocysts.

During the procedure, a speculum is inserted in the vagina to identify and locate the cervix. Then a soft transfer catheter containing one or two embryos is inserted through the cervical canal into the uterine cavity. This procedure may be guided by ultrasound to increase accuracy of placement, which should be about 1-2 cm below the uterine fundus. Once proper catheter placement has been achieved, the embryos are deposited into the uterus. Anesthesia is not required for this procedure, but may be indicated in certain cases.

Gonadotropin releasing hormone agonists usage and treatment with a combination of follicle-stimulating hormone and luteinizing hormone can also facilitate pregnancy for women who undergo Frozen-Thawed Embryo Transfer.

Single-embryo transfer has been shown to have better outcomes in terms of gestational age at delivery, birth weight, and mode of delivery (i.e. caesarean or vaginal delivery). Rates of multiple gestation are also lower, which avoids the moral and ethical challenges associated with such an occurrence.

The chances for success are promising: Research has demonstrated a survival rate of almost 80% for embryos transferred after the thawing procedure. Also, women whose endometrial thickness is at least 8 mm on the day of embryo transfer have a higher pregnancy success rate than women with a smaller endometrial thickness.