How does embryo freezing (cryopreservation) work?

During in vitro procedures, there are sometimes extra embryos which sho uld be frozen for future attempts. There is a strict criterion followed for freezing embryos since the freezing and thawing procedures of embryos can be too aggressive.

This process does not modify or alter the quality of cryopreserved embryos. The Vitrification technique has increased exponentially the number of good quality embryos with respect to the transferred “fresh” embryos, as this freezing technique is lighter on the embryos (compared to the slow freezing procedures), hence obtaining a higher rate of survival and pregnancy.

Those patients that have vitrified embryos are contacted every 2 years to confirm that they still wish to keep their frozen embryos for future attempts. The embryos belong to the patient and it is the Clinic’s mission is to ensure safekeeping.

Why can we not always freeze the embryos left over from a fresh cycle?

We can freeze embryos in the majority of fresh cycles carried out. We place the leftover embryos in a culture medium to monitor their evolution and Biologists will determine whether they can be frozen or not. The freezing criteria are different to the criteria to evaluate the transfer of fresh embryos: they must meet much more specific requirements as the freezing and thawing can potentially be an aggressive process for embryos.

If we were to freeze all of the leftover embryos, the cancellation rates of a transfer after thawing would be very high. Therefore we do not freeze all the embryos that are left in the laboratory after a fresh transfer. In spite of these requirements, there is around an 8% cancellation rate for cryotransfer after the thawing and re-adaptation in a culture medium of the embryos.

Is there any connection between the cryopreservation of embryos and pregnancies occurring from the fresh embryos transferred from the same cycle?

It is more difficult for the embryos to develop in the laboratory than in the mother’s uterus. According to studies carried out, there is no connection between freezing embryos and the pregnancy rate from fresh embryos. Therefore, if we cannot freeze part of the leftover embryos, this does not mean you are any less likely to become pregnant or vice versa.

How long can my embryos remain frozen for?

50 years old has been confirmed as the limit for a woman to carry out an Assisted Reproduction Technique. We will regularly ask you (every 2 years) if you still wish to keep your frozen embryos in order to try again in the future. The length of time that embryos are frozen for does not affect their quality.