There are two main embryo transfer protocols: the natural frozen embryo transfer (FET) cycle and a medicated FET cycle.
A natural FET cycle is performed when a woman has regular menstrual cycles and ovulation. A woman’s menstrual cycle is monitored and the embryo transfer is timed around the natural ovulation. Sometimes a natural FET cycle may be supplemented with a human chorionic gonadotrophin (hCG) injection to aid a more precise ovulation period for transfer.
During a medicated FET cycle, oestrogen and progesterone medication is administered to aid in thickening the uterine lining to make it receptive to the embryo. Medication is also given to suppress a woman’s natural cycle and prevent ovulation. Oestrogen and progesterone medication is continued until a positive pregnancy test and also for the first 12 weeks of pregnancy.
In comparison to medicated FET cycles, natural FET cycles require more monitoring and ultrasound scans (approximately 3-4 scans) as they are more difficult to predict. Medicated FET cycles are more controlled, meaning it is easier to get the timing right for embryo transfer.