Experience has shown that high quality embryos are far more likely than others to survive and be capable of further development after cryopreservation. Embryos that divide slowly, or are irregular in other ways, do not fare well after cryopreservation and, therefore, are not frozen.
Cryopreservation Of Embryos, Sperm, And Oocytes
How Does Cryopreservation Work?
Cryopreservation is a technique used by IRMS to freeze and then thaw eggs, embryos or sperm for use in in vitro fertilization (IVF) cycles. Thawed sperm may also be used in IUI (intrauterine insemination) treatment cycles. With the availability of frozen embryos, a woman doesn’t need to undergo stimulation by fertility drugs in order to have an embryo transfer during an infertility treatment cycle.
During the standard course of infertility treatment, hormones are used to stimulate the development of multiple eggs. After these eggs are retrieved and fertilized in the laboratory, there may be more embryos created than can reasonably be transferred to the woman’s uterus. When these “extra” embryos are of sufficient quality, they may be cryopreserved (frozen) so they may be transferred at some future date. Embryo cryopreservation, which is possible in approximately 60% of IVF cycles at IRMS, provides the opportunity to have an additional embryo transfer without the inconvenience and expense of an additional IVF cycle.
Embryos may be cryopreserved at any stage between day 1 and day 7 after egg retrieval. However, not all embryos are candidates for cryopreservation.
Problems such as these are more prevalent in older women. After placing the embryos in a cryoprotectant solution, they are flash cooled at a rate greater than 10,000 degrees C/minute in a process called vitirfication. Long-term embryo storage is in liquid nitrogen at a temperature of -320 degrees˚F (-196 degrees˚C)
Cryopreserved embryos are replaced during either a natural menstrual cycle or a hormonally controlled cycle. Considerable care is taken to minimize the possibility of damage caused by cryopreservation. Typically, embryos survive warming after vitrification at rates exceeding 90%. For oocytes, the post-vitrification survival rate is 85-90%.
Extended periods of storage in liquid nitrogen have no apparent effect on their viability. Embryos thawed after several years of cryostorage fare as well as those frozen for only one or two months. Since 1983, the cryopreservation procedure has resulted in the birth of thousands of babies worldwide.
Major advances have been made in the past several years in our ability to freeze human oocytes (eggs) and we now routinely freeze eggs as an elective option for women who seek to delay childbearing or who are looking to preserve their fertility as a result of a medical diagnosis such as cancer.
Vitrification is a newer and more advanced cryopreservation technique where eggs undergo rapid freezing, not allowing time for ice crystals to form. Vitrification of eggs involves newer cryoprotectants that have high concentrations of “anti-freeze” like products. In order to do successfully, the technique involves a fair amount of experience and expertise. The oocyte is first placed in a bath with a lower concentration “anti-freeze-like” cryoprotectant, along with sucrose (sugar) to help draw some of the water out of the egg. Then, the egg is moved into a high concentration of cryoprotectant for less than one minute and immediately placed in a liquid nitrogen bath (minus 320 degrees Fahrenheit) which instantaneously freezes the egg. When the woman is ready to attempt pregnancy, the egg is rapidly warmed and the cryoprotectant is washed away.
With vitrification, it is now possible to cryopreserve the human egg as successfully as it has been to cryopreserve embryos.