Stimulation of ovaries to promote egg production during fertility treatments often result in more embryos being created than what can be transferred into your uterus in the same treatment cycle. Regardless of the day of your embryo transfer, with your permission, we always try to grow all excess embryos to the blastocyst stage, as it is at this stage that we normally freeze embryos.
Embryo freezing (Cryopreservation) is available to patients who have excess good quality embryos which have reached the blastocyst stage either on day 5 or 6 after egg collection. With few exceptions, we only freeze embryos that have reached the blastocyst stage, in order to maximise your chances of success in a later Frozen Embryo Replacement cycle (FER). It is only at the blastocyst stage that we are able to determine the presence of, and assess, the structures necessary to give rise to pregnancy: a group of cells which will give rise to the fetus, the Inner Cell Mass (ICM) and cells which will form the placental cells, the Trophectoderm.
Both partners will need to give permission if you wish to consider freezing suitable and surplus embryos. The Nurse Coordinator will help you complete the necessary consent forms at your Treatment Information Appointment (TIA) at the commencement of your treatment cycle. Freezing your excess good quality embryos will give you the opportunity to return for a Frozen Embryo Replacement (FER) cycle at a later date, hopefully when trying for more children, or alternatively if your fresh treatment cycle has failed. The Frozen Embryo Replacement cycle has the benefit that the embryos are thawed and replaced into the uterus at the same corresponding stage in the cycle as when they were frozen, this time without the need for ovarian stimulation or egg collection.
At the Herts & Essex Fertility Centre we use the method of vitrification to cryopreserve or freeze suitable blastocysts. This latest technique serves to rapidly cool the embryos, leaving them free from ice crystals which can otherwise damage their structure. This method of freezing enables 80% of patients to progress to embryo transfer in a Frozen Embryo Replacement cycle.