(CNN) -- Freezing a woman's eggs should no longer be considered "experimental," according to the American Society of Reproductive Medicine, a move that signals the technique is now standard for infertility treatment.
The society reviewed data from four randomized controlled trials and various observational studies that compared fertilization rates, embryo implantation rates and pregnancy rates of fresh eggs versus eggs that were frozen using a method called vitrification.
Overall, frozen (or vitrified) eggs had fertilization rates between 71 and 79%, implantation rates between 17 and 41% and clinical pregnancy rates (positive pregnancy tests) between 36 and 61%.
The data also showed no increase in birth defects, developmental disorders or chromosomal abnormalities when in vitro fertilization cycles were conducted with frozen eggs, leading the society to declare the technique effective and safe.
"The technology and technique are getting better, and success rates are good," said Dr. Samantha Pfeifer, chairwoman of the American Society of Reproductive Medicine's practice committee. "So with those studies, we felt comfortable saying there is a lot of information on how oocyte cryopreservation is improving."
"Vitrification is basically the solidification of a solution without ice crystallization," said Dr. Zsolt Peter Nagy, embryologist and scientific director at Reproductive Biology Associates in Atlanta. "And that's very important."
The lack of ice crystallization is key to the health of the egg because, as Nagy explained, "ice crystallization that happens during slow freezing is the biggest danger for egg ... cryopreservation because ice crystals can damage the cell membranes, and it results in the degeneration of the eggs.
"In vitrification, there is no ice crystallization, so basically, you avoid that problem."
Egg freezing has been marketed as a means for women without fertility issues to preserve their fertility beyond their peak childbearing years. Yet the American Society of Reproductive Medicine says its decision to drop the "experimental" label should not be interpreted as an endorsement for women without infertility issues to freeze their eggs for future use.
"We think we should proceed cautiously in using this as an elective technique, especially in older patients," said Dr. Eric Widra, chairman of the Society for Assisted Reproductive Technology practice committee.
"There is an inherent conflict between the desire to freeze eggs and the need to freeze eggs. Freezing eggs for the future sounds like a good insurance policy but may not be an insurance policy that needs to be cashed in."
Widra says that the best way to conceive is still through natural intercourse at an appropriate age and that vitrification should be reserved for women and couples with urgent infertility needs, like patients with medical indications that they will lose their fertility (perhaps a woman with cancer or a specific genetic condition), couples going through IVF who don't have sufficient sperm or couples who are unable or unwilling to freeze embryos.
Other fertility specialists disagree, arguing that fertility is different for everyone and that women should consult with their doctors if they decide to put off pregnancy until their mid- to late 30s.
"Women unfortunately are getting married later, having children later, facing more infertility problems," explained Nagy.
"Doing fertility preservation by egg cryopreservation is an option for them today. It was not an option in the past, but today it is an option."