IVF (in vitro fertilization) is a process of removing a woman's eggs by way of surgical procedure and pairing with a man's sperm in a controlled laboratory environment; embryo(s) are then eligible for transfer or cryopreservation (freezing) after several days of development in the laboratory. Prior to egg retrieval, a combination of medications (FSH & LH) is given to stimulate the ovaries to produce multiple eggs. Many eggs are desirable as some will not fertilize or develop to maturity. Monitoring of the maturation of the oocytes and the endometrium of the uterus are accomplished by ultrasound as well as measurements of estradiol and progesterone hormones in the blood. This is a process that requires meticulous adherence to medication protocol and frequent visits to the clinic and laboratory for monitoring in order to ensure procedures are performed in best timing for optimal outcomes.
FET (frozen embryo transfer) is the process of thawing and transferring previously-created embryo(s) into a woman's uterus. Many couples are fortunate to have embryos in excess of those chosen for the original transfer. Unless other arrangements have been agreed to, these "surplus embryos" are typically frozen in liquid nitrogen to allow another pregnancy attempt at some future time. As a result, many couples have an opportunity to attempt another pregnancy at a fraction of the cost and involvement physically of a "fresh" IVF cycle as the embryos are already "created".