The freezing of embryos and sperm has long been recognized as a means of pursuing fertility treatments later in life. However, new techniques involving the cryopreservation of eggs have recently resulted in greater success. Pregnancies and deliveries have now been reported after the thawing and fertilization of frozen eggs.
Candidates for egg freezing
It is known that fertility declines with advancing age in women. This is largely due to the increase in the percentage of embryos with chromosome abnormalities that occur with age. Egg freezing may be especially useful for cancer patients. Unfortunately for these women of childbearing age, treatments such as chemotherapy and radiation have been shown to cause damage to maturing follicles in the ovaries. If a woman who is diagnosed with cancer has a male partner with whom she wishes to conceive but is not ready to attempt pregnancy, it is better for them to create embryos through IVF and freeze the embryos (embryo cryopreservation).
Embryo cryopreservation has been performed successfully for many years and is currently considered the gold standard in fertility preservation. However, some women may not have a partner that they want to have children with or are too young to have partners. These women are also candidates for egg freezing.
Method for Frozen Eggs
The egg retrieval process for oocyte cryopreservation is the same as that for in vitro fertilization. This includes one to several days of Hormone injections that stimulate ovaries to ripen multiple eggs. When the eggs are mature, a medication to trigger ovulation is given and the eggs are removed from the body using an ultrasound-guided needle through the vagina. The procedure is usually conducted under sedation. The eggs are immediately frozen.
Eggs (oocytes) are frozen using either a controlled-rate, slow-cooling method or vitrification. Once frozen, the zona pellucida or shell of the egg hardens. Thus, when eggs are thawed, a special fertilization procedure is performed by an embryologist whereby sperm is injected directly into the egg with a needle (ICSI) rather than allowing sperm to penetrate naturally by placing it around the egg in a dish.