In an IVF cycle, usually more embryos are developed than those that will be transferred. If embryo quality is appropriate, they can be cryopreserved (frozen) and used in a future cycle. In this way, the couple can make more than one attempts with only one cycle of ovarian stimulation for oocyte production.
Embryo cryopreservation is a technique that some couples may reject for ethical, philosophical or religious reasons. In any case, the official position of the Church of Greece is not against cryopreservation.
Embryos can be frozen on the 1st, 2nd, 3rd or 5th day after oocyte retrieval. Embryologists assess them based on international criteria and estimate which embryos are viable and can yield a pregnancy. These embryos are suitable for cryopreservation, which we recommend, as it increases total pregnancy achievement rates. At “gennima”, only good quality embryos are frozen, because mediocre or bad quality embryos usually don’t survive at thawing. If embryos are mediocre, we suggest that cryopreservation should be avoided, as it would simply increase the couple’s expenses, with no actual hope of achieving pregnancy with those embryos.
If embryos are cultured until the blastocyst stage, usually there are no redundant blastocysts to be cryopreserved (the best embryos are selected via blastocyst culture). Embryos can remain frozen for 5 years, under the appropriate conditions of cryopreservation. At “gennima”, survival rates after freezing/ thawing reach 80%. In any case, the couple discusses with the doctor on “whether” and “when” the embryos will be cryopreserved and decision is made jointly.
The method of cryopreservation actually increases pregnancy achievement rates without repeating stimulation, because if the cycle with the “fresh” embryos doesn’t succeed, there are many chances for the cycle with the frozen embryos to have a positive outcome. Besides, many clinical researches show that pregnancy achievement rates don’t vary depending on whether fresh or frozen embryos are transferred (when the number and quality of embryos are taken into account). Even if pregnancy is achieved following the first treatment, the couple may use the embryos for a second pregnancy, to give their first child a brother or sister.
Another self-evident question is related to the health of children born following cryopreservation. The safety of cryopreservation has been proved in many studies: embryos can remain frozen for long periods of time and give healthy pregnancies later on.
A recent research presented to the ESHRE (European Society of Human Reproduction and Embryology) has studied whether children born following cryopreservation risk having more congenital abnormalities than children born following classic IVF or ICSI with no cryopreservation. The research has been carried out in Denmark and included almost 1.300 children born followng cryopreservation and more than 17.000 children born by means of IVF (classic or ICSI) with no cryopreservation. No difference has been detected among children regarding the occurrence of congenital abnormalities. In fact, it has been noted that sometimes, cryopreserved embryos might even prevail; e.g. it has been claimed that conditions may be better when they are transferred in the uterus, as at that time, the woman’s hormone levels are closer to normal than when fresh embryos are transferred and the patient’s hormone levels are increased due to ovarian stimulation treatment.
Pinborg A et al. Danish national controlled cohort study on neonatal outcome of 1267 children born after transfer of cryopreserved IVF and ICSI embryos in 1995 to 2006, ESHRE Meeting 2008; Abstract O-122
‘Infant outcome of 957 singletons born after frozen embryo replacement: The Danish National Cohort Study 1995–2006’
published online 31 July 2009
In any case, as in all assisted reproduction methods, more clinical studies including large children populations, are required, so as to confirm the existing studies, as well as to thoroughly examine all the parameters of this method. Cryopreservation has definitely contributed to the increase of the assisted reproduction methods’ success rates.
Please read a relevant review of 2009, confirming the safety of cryopreservation:
‘Children born after cryopreservation of embryos or oocytes: a systematic review of outcome data’
Human Reproduction, Vol.0, No.00 pp. 1–16, 2009