How does embryo freezing (cryopreservation) work?

Published: 16 March 2017|Last updated: 30 November 2020|

During In Vitro Fertilisation cycles, when we have several good quality embryos, it is necessary to cryopreserve these surplus embryos, which are then saved for future attempts. The criteria that the embryos must meet in order to be frozen are very strict, since the freezing and thawing processes can be detrimental to these embryos.

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), thus 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 to ensure safekeeping.

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. Despite these requirements, there is a certain percentage of cryotransfer cancellation after thawing and a period of readjustment in culture medium that is lower than 5%.

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.

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.

The cryopreservation of embryos is the best way to preserve those embryos that have been the outcome of an in vitro fertilisation treatment, whether it is because once the fresh transfer has been carried out there are surplus embryos of good quality, or because for different reasons it is necessary or advisable to perform the transfer at another time.

This technique optimises the assisted reproduction treatment used by increasing the pregnancy rate by means of puncturing, since with just one cycle of ovarian stimulation, embryos can be transferred more than once. In addition, the cryopreservation of embryos also contributes to reducing the risk of multiple pregnancies, since it gives you the option of not having to transfer all the embryos at once, but rather, depending on the characteristics, they can be preserved and have several chances for transfer.

It is a strongly recommended technique for patients who have undergone a highly complex assisted reproduction treatment and have embryos that cannot be transferred fresh as they exceed the established quantity (currently Spanish legislation allows the transfer of up to a maximum of 3 embryos). Also, in those who, regardless of the quantity of embryos obtained, decide not to undergo a fresh transfer, whether of their own choice, or for medical reasons. Finally, another indication for the cryopreservation of embryos or gametes would be cases in which one of the members of the couple suffers from a disease that will prevent them from obtaining gametes later on (such as patients who must undergo chemotherapy treatment) in order to undergo another full assisted reproduction cycle in the future.

If you need more information, do not hesitate to consult our professionals.

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