The precious embryos that are not used in in vitro fertilization cycles that are cryopreserved are referred to as frozen embryos. Establishing a pregnancy using them is referred to as frozen embryo transfer (FET) or a thaw cycle. A normal uterine cavity is prepared prior to a frozen embryo transfer to maximize the possibility of a successful pregnancy.
Tests Prior to Considering Frozen Embryo Transfer
Before a frozen embryo transfer is performed, a woman is tested to ensure her uterine cavity is normal. Three tests are typically done to assess the uterine cavity. One is a hysterosonogram where the uterus is injected with saline and viewed with ultrasound. Another is hysteroscopy, when a fiberoptic telescope is placed in the uterus to see the cavity. Another is HSG with x-ray dye injected into the uterus so the cavity can be seen in x-rays. If an abnormality is seen, doctors attempt to surgically correct it prior to frozen embryo transfer.
Preparing for Frozen Embryo Transfer
Once it is determined the uterine cavity is ready, hormones are used to prepare the uterus for frozen embryo transfer. The pituitary gland is suppressed to minimize the possibility of ovulation, typically by giving the woman Lupron injections. Then the hormones progesterone and estrogen are used the mimic the changes that happen during menstruation.
The estrogen thickens and matures the uterine lining and can be administered through injections, pills, patches or vaginally. The woman is monitored through ultrasound and blood tests during this period. Because it is not a fresh IVF cycle, the cycle is flexible and less stressful on the woman.
Once the lining is thick, progesterone is administered and Lupron ceases. The progesterone helps by maturing the uterine lining so it is receptive to the implantation of an embryo. The development of the uterus and the stage of the embryo must match so the transfer needs to be done on a particular day. Women with regular menstruation cycles can have a frozen embryo transfer done without hormone preparation.
When the egg is fertilized, it is grown in the laboratory for three to six days with cryopreservation done on embryos in all stages of development. Immediate freezing often means the survival after thawing is high. Often multiple embryos are transferred to produce pregnancy. Couples have successfully conceived healthy babies because of frozen embryo transfer. Typically embryos are frozen for two to five years but can be frozen longer and is considered safe for the baby.
This article is for informational purposes only. We are not doctors.