Frozen embryo transfer (FET) is a procedure when embryos frozen in an earlier IVF/ICSI cycle are thawed in the current cycle, and transferred. It can be done in natural and stimulated cycles. Natural cycle is chosen when a young women is ovulating regularly and there is no need for using exogenous estradiol or progesterone. The patient is scheduled for her first ultrasound check around day 10 of the cycle. The thickness of the endometrium and the existence of the leading follicle are determined during this visit. After this exam the day for the embryo transfer can be determined by measuring LH or by serial follicle ultrasounds.
Frozen embryo transfer (FET) can also be done in a cycle stimulated by exogenous estrogen pills. A woman uses estrogen pills (e.g. Estrofem 2mg), usually three times a day from day 1 of the cycle. Stimulation is needed if a woman had thin endometrium or unfavorable estrogen levels previously, if she does not ovulate, is over 38 years of age, or to select the best timing for FET. Follicle ultrasound is usually done on the tenth day of the cycle. Next, the patient starts taking progesterone (e.g. Utrogestan 3x200mg). Embryo transfer is done several days after the patient start taking progesterone.
If a procedure is successful, a patient continues taking estrogens and progestins until at least week 8 of pregnancy.