Based on current HFEA (Human Fertilisation and Embryology Authority) guidelines, only two embryos (or a maximum of three if the woman is over 40) may be transferred after a treatment cycle.
If the treatment produced more than two (or three) good quality embryos, those that aren’t used may be frozen for future use. These embryos will be frozen at extremely low temperature, which ensures that they do not deteriorate over the number of years they are stored.
In a Frozen Embryo Replacement Cycle the woman takes medications to prepare her womb to receive these embryos. The advantage of this treatment is that there is no need to use hormone injections to stimulate the ovaries.
An ultrasound scan is performed to assess the lining of the uterus to determine whether it is ready to receive the embryo. Once the lining is ready, embryos are thawed and transferred.