Embryo cryopreservation

With cryopreservation, embryos may be preserved usually for 5 years, therefore, if an IVF attempt is unsuccessful, they can be used in the future after thawing. On the other hand, in cases with successful IVF, the remaining cryopreserved embryos may be used on a future date, when the couple will decide to have more children. The pregnancy rate of cryopreserved transferred embryos is equally high, whereas cryopreserved embryos are not impaired by the procedure since they are protected by the addition of cryoprotectant substances which prevent the formation of harmful salt and crystals. The embryos are preserved in liquid nitrogen.

The whole procedure of cryopreservation lasts a few hours, whereas thawing needs 30 – 45 min. Embryos cryopreserved for 13 years have been successfully thawed, whereas clinical pregnancy has been succeeded with embryos preserved for 9 years. Healthy babies have been born after 5 years of cryopreservation.

Embryos frozen at the 2 PN stage have a higher chance of survival to those frozen at a later stage. Pregnancy rates are usually affected by various factors. Age does not seem to consist an adverse factor, although older women do not produce many eggs, needing cryopreservation.

Blastocyst stage embryos (5 days) form a special category and are in need of extra care in cryopreservation to avoid any damage. Newly developed methods, however, provide better survival to these embryos and promising pregnancy rates, resulting in healthy babies.  Many studies showed that babies born from cryopreserved embryos do not present growth disorder or congenital abnormalities to normally conceived babies.

In addition, the method of cryopreserving embryos overcomes the possibility of ovarian hyperstimulation syndrome (OHSS), a rare but severe complication of the luteal phase of the cycle or early pregnancy. In the presence of OHSS, pregnancy must be avoided since it may cause severe medical problem.

Finally, the method of embryo cryopreservation provides an increased possibility of pregnancy success when fresh embryos attempts were unsuccessful, or when the couples want more children after a previously successful IVF attempt.