Cryopreservation - Embryo Freezing

Cryopreservation of embryos

The basic variable to be considered in embryo cryopreservation (freezing) is the embryo (fertilized female egg) itself. There are differences in the freezing sensitivity of embryos of different grades or "quality". Only embryos of the best grades are actually freezable. Poor quality embryos may even be discarded rather than being frozen to yield unacceptable low pregnancy results. The pregnancy rate percentage of frozen embryos is indeed less than that of fresh embryos; but the proportionality of pregnancy to embryo grade appears to be the same for both fresh and frozen embryos.

The embryonic stage has also been considered as an important variable of cryopreservation. The disposition of any frozen embryos that are not transferred in an IVF cycle must be arranged in writing before cryopreservation. In the event that a successful pregnancy is established following a fresh or frozen embryo transfer, it is the discretion of the couple as to whether the remaining frozen embryos should be stored, or appropriately discarded or donated.

Embryo Freezing Technique

Different solutes have been used to protect human embryos against freezing damage. Embryos are then frozen using the techniques of a controlled rate freezer. The primary concern with the use of cryopreservation techniques is the possible loss of embryos to the stress of freezing and thawing techniques. To increase successful embryo cryopreservation, mechanical process is controlled. A back-up freezing system is always available and a generator back-up power is available in the event of power outage. The Ethics Committee of the American Society of Reproductive Medicine (ASRM) has published guidelines for ethical human embryo cry preservation.

Possible advantages of cryopreservation of embryos suggested by the ASRM include:

1. Reduction of the risk of triplets or quadruplets by cryopreservation of embryos exceeding an optimal number for transfer to and individual patient.

2. Possibly increasing pregnancy rates by replacing thawed embryos during spontaneous ovulatory cycles in which the estrogen and progesterone hormone levels do not exceed that which occurs naturally.

3. Possibly decreasing the number of stimulated ovary drug treatment cycles needed for the attainment of pregnancy.

 

Last updated: August 11, 2008
Reviewed by Dr. Rachel McConnell and her medical staff