When a woman wishes to become pregnant, the vitrified eggs would be warmed and then fertilized with male sperm. The fertilized eggs would then be transferred to the uterus in the same procedure that's used successfully when couples freeze embryos.
When eggs are warmed after vitrification, fertilization rates with conventional IVF are low. Instead, researchers have found, a single sperm cell must be injected into a single oocyte, a technique called intracytoplasmic sperm injection, or ICSI. While ICSI is an established technique used in assisted reproduction, it is more complex and costs more than traditional methods.
Using mouse oocytes, 80 percent of eggs that had been vitrified became fertilized with ICSI, with a live birth rate of about 30 percent, comparable to conventional IVF when eggs are not frozen. The fertilization and birth rates for vitrified eggs are similar to the rates for control eggs that were not vitrified.
For egg freezing to work, it must be a mature oocyte, which means a woman must have 14 days of hormone treatments to stimulate mature egg production. This could limit its applications for some women. Researchers question if it is appropriate for women with cancers fueled by estrogen, such as breast cancer. In addition, the hormone treatments require delaying the start of cancer therapy, which may not be an option for every patient.
Guidelines for patients and physicians still need to be established as the technique begins to be offered in a clinic setting, Smith says. "This is a very new technology and it requires education both of patients and physicians," Smith says.
U-M has cryopreserved eggs for one patient; h
Source:University of Michigan Health System