Egg freezing has come a long way since it was first introduced as an experimental technique in the 1980s.

Today, the average age of women giving birth for the first time has risen to 28 as more women delay having children, making egg freezing an attractive option for those who would like to postpone pregnancy. And with companies like Apple and Facebook offering employees $20,000 to freeze their eggs, the option could be attractive to women who are looking to further their careers.

Cryopreservation is by no means in its infancy, but it was only deemed nonexperimental in 2013 by the American Society for Reproductive Medicine. Although egg freezing is being hailed as the answer for women who would like to postpone pregnancy, just how successful is in vitro fertilization involving frozen eggs?

The answer: It's complicated. But a new study released by the Journal of the American Medical Association may offer some insight.

The study gathered data from 380 fertility clinics across the U.S. that accounted for 92 percent of all in vitro procedures performed in 2013. Researchers from the Center for Human Reproduction looked to compare the number of live births that resulted from fresh donor eggs and frozen donor eggs.

The study looked at 11,148 in vitro cycles, of which 20 percent of the women used donor eggs. There was a 49.6 percent success rate from the fresh eggs compared to a 43.2 success rate of the fresh donor eggs.

When the researchers factored in the number of live birth rates per embryo transferred, the difference widened to a 47.1 percent live birth rate from women who used frozen eggs and a 56.1 percent live birth rate for women who used fresh eggs. The reason for the difference, however, could be due to a number of factors.

Egg donors are carefully selected by fertility clinics and usually consist of women in their 20s since they have the most viable eggs. Only recently have fertility clinics begun freezing unfertilized donor eggs.

In the past, technicians would fertilize the extracted donor eggs immediately, then freeze the fertilized embryos for later use. The process of freezing unfertilized eggs is fairly new, and the freezing and thawing process is complicated and must be precise.

The eggs themselves are cells full of water. Once that water freezes, it forms sharp crystals that are capable of poking holes in the cell. The chromosomes are also stretched during freezing, leaving them vulnerable to breakage.

In addition to the complications that can arise during the freezing and thawing process, frozen donor eggs may not be implanted in the same numbers as fresh eggs. Six to eight frozen donor eggs are typically used during an in vitro cycle, compared to 15 to 25 fresh eggs used in one cycle. This significant difference could have affected the data in the new study.

Before accepting that fresh eggs are better than frozen eggs for in vitro, the limitations of the study must be considered. All of the women included in the study were anonymous, therefore age, infertility issues and the stage at which the embryo was implanted were not factored. It is also important to note the study only included donor eggs, not the birth rate for women who had frozen their own eggs.

Doctors noted that additional studies are needed to determine the true success rates, and frozen eggs may actually be a better option for many women. Frozen eggs cost half as much as fresh eggs, and they are more readily available.

For a fresh egg to be successfully implanted, the recipient and the donor's cycles have to match up almost perfectly. Frozen eggs can be stored then implanted when it is most convenient for the recipient.

The data for live births of women who are flocking to fertility clinics — usually in their 30s and 40s — to freeze their own eggs is yet to be determined. A past study has shown that women should store their eggs by age 35 in order to have a successful outcome.

Egg donors are usually in their 20s, and eggs begin to degrade with age, lowering the chances of a successful outcome. Researchers will have to wait for enough women in this age range to use their own frozen eggs in order to collect their birth rate data.