Cryopreservation of Human Embryos

The process of cryopreservation involves the freezing and storage of embryos at -196 degrees Celsius in liquid nitrogen. Human and mammalian tissues can often be frozen for prolonged periods of time and function normally after thaw.

For many years the process of cryopreservation has been successfully used in the reproduction of various animal species. Cryopreservation has been applied to IVF for several reasons. First, as the success with IVF has improved, the prevalence of multiple births also has increased. Twins or triplets (or more) are at increased risk for problems before or after delivery, including pre maturity and birth defects. It is now clear that the incidence of multiple births can be limited by decreasing the number of embryos transferred. There is a trade-off, however. We know that the pregnancy rates increase when we transfer up to four embryos. The policy of most IVF programs doing cryopreservation is to transfer the three or four best embryos and try to preserve the remaining embryos for a transfer during a subsequent cycle. In this way, the chance of pregnancy during the first cycle is maximized with some control over the maximum number of implantations which might occur.

Although the numbers are small, children have been born from frozen embryos. It appears that there are no increased risks during pregnancy when compared to fresh embryos. However, the risk remains that, when thawed, embryos may be abnormal and therefore unusable, or that embryos might develop abnormally after transfer into the uterus. Embryos are examined microscopically for abnormalities, and all the procedures available for the discovery of abnormalities which are customarily used for IVF will be performed. The potential for multiple births exists following replacement of one or more thawed embryos into the uterus. Early evidence from cryopreservation worldwide reveals no increased risk of a major abnormality in the babies born through this technique.

Risks to the patient of the placement of thawed embryos in the uterus are similar to the risks of embryo transfer during a normal IVF cycle.

Transfer Procedure

A cycle in which frozen embryos are transferred is much simpler than a normal IVF cycle. The only medications used are estrogen and progesterone. There will be certain days during the cycle that blood will need to be drawn for estrogen measurement and a scheduled day for a vaginal ultrasound. Should you desire cryopreservation and a subsequent embryo transfer, a detailed instruction sheet will be given to you.

Pregnancy Rate

Our cumulative ongoing/delivered pregnancy rate for 1996-1998 was 27%. Please view our IVF Success Rates for our latest statistics.