Cryopreservation of embryos.

As previously mentioned about 1/3 of all IVF treatments result in spare embryos of good quality that could be used for cryopreservation. These embryos can be replaced after thawing at a later stage. This could be the case when the couple would like more children after their first successful IVF treatment or when the first fresh IVF cycle has not resulted in a pregnancy. The advantage of this kind of treatment is that no hormonal stimulation of the follicles to recruit oocytes is necessary. No oocyte retrieval has to be performed.

The crucial factor in cryopreservation is to avoid ice formation within the embryo during freezing. The ice crystals might damage the cellular structure and by that seriously affect the viability of the embryo. To avoid crystallization the embryos are placed in a solution driving the water contents out of the cells. By this the crystallization is minimized. The cryopreservation itself takes 2-3 hours and ends at a very low temperature. Cryopreserved embryos are stored at -196°C. At this stage the embryos are in a static condition and no aging or other activity takes place inside the embryo. It has been found that the embryos can be cryopreserved up till 10 years without any negative effects in the offspring. Swedish legislation allows cryopreservation for 5 years.

IVF Öresund has a special programme when replacement of previously cryopreserved embryos is to take place. This scheme calls for suppression of the pituitary hormone production for a period of 2-3 weeks. When the spontaneous hormone production is at a very low level, oestrogens are administrated as tablets to stimulate the growth of the endometrium. After approximately 17 days of hormonal replacement the embryo transfer of the previously cryopreserved embryos is scheduled. A couple of days before supplementary treatment with Progesterone has been started. This is necessary as no spontaneous Progesterone production will take place, no ovulation has occured.

Replacement of previously cryopreserved embryos gives a chance of pregnancy of roughly 35% after replacement. Cryopreservation of embryos is a tough procedure for the embryos. One has to calculate that about 25 % of all cryopreserved embryos will not survive after thawing. This is an all or none situation, meaning that those embryos that show normal vital signs will, if giving rise to pregnancy, not have an increased risk of miscarriage or chromosomal abnormalities.

Cryopreservation is a most valuable complement in all subfertility treatments. Cryopreservation could be used not only in the situation of spare embryos but also when storage of sperm or testicular or ovarian tissue is necessary.