IVF attempts often involve the creation of a high number of embryos, particularly in the cases of young couples. Several good quality embryos may remain following embryotransfer. These embryos can be preserved in a frozen state, so that they can be transferred to the uterus at a later stage. Cryopreservation is also used when it is concluded that - during the IVF cycle - the endometrium is not sufficiently prepared to accept the embryos, or in the case of ovarian hyperstimulation, when it is decided to perform embryotransfer at a second stage.
Embryos are cryopreserved in the so-called hermetically sealed straws.
Their temperature is gradually reduced down to -196°C (liquid nitrogen temperature) with the use of special equipment. The straws are stored in special liquid nitrogen containers. Embryo freezing in such conditions can be extended for a long period (up to five years). The couple is thus able to use the embryos in the future, without a need for a repeated ovarian stimulation, egg retrieval and IVF procedure.
These embryos can be defrosted and transferred to the uterus during a later cycle. This cycle simply involves the administration of medication to prepare the endometrium, followed by the embryotransfer. Couples sign an "IVF agreement" where the rules applying to embryo freezing are specified. The same agreement is also signed by the embryologist who performed the freezing and is maintained in the records of our laboratory.
The rules are as follows:
• Since cryopreservation involves the constant consumption of nitrogen, a rather expensive liquified gas, the couple share part of the cost. The relevant amount is paid in advance for a period of one year.