A lab worker places a test tube in a container used to freeze human eggs at a fertility clinic in Athens. (Kostas Tsironis/Bloomberg)

When Apple and Facebook announced last year that they would cover elective egg freezing for their female workers, the companies sparked a lot of curiosity about this procedure. The ability to put motherhood on hold by preserving your eggs for future use seemed like an alluring way to ease the babymaking pressure for couples who are meeting and marrying later in life.

But a quick search into elective egg freezing reveals confusing and often conflicting information. For starters, the women going through this process are not all workaholics looking to delay motherhood because of their taxing schedules. In fact, in one survey conducted by researchers at New York University, 88 percent of women who froze their eggs cited the lack of a partner as one of their reasons for delayed childbearing.

Motivations aside, one 2010 study found that at least 50 percent of in vitro fertilization (IVF) clinics in the U.S. offered elective egg freezing. And since the label “experimental” was lifted from the procedure two years ago, that number has probably grown. That means you’re more likely now to find a place to freeze your eggs — but first you need to know the facts.

Link between age and cost

While experts’ opinions differ, the best age to freeze your eggs is between 31 and 33, according to one study.

“Below age 31, the success rates are high,” says Tolga Mesen, a doctor at UNC Fertility in Raleigh, N.C., and a co-author of the study, “but the success rate is also high if you try to conceive naturally.” Thirty-two seems to be the point at which egg freezing makes a significant difference in your potential to get pregnant later in life.

In practice, the average age tends to be late 30s, says Elizabeth Fino, a reproductive endocrinologist from NYU Langone Medical Center in New York, who has seen the age of her patients drop from 38 or 39 in 2010 to 36 or 37 in 2014. She encourages women who may be interested in egg freezing to consider the importance of age. “If you’re going to invest that amount of money, you want to make sure you’re in the best success-rate group.”

The procedure is quite an investment. “In general, the cost will be between $10,000 to $15,000 to freeze your eggs,” says Ilaina Edison, chief executive of Extend Fertility, a company that works with fertility centers to offer egg freezing. That price is an estimate for a woman about 35 years old; it includes a hormone treatment, one cycle of egg retrieval and one year of egg freezing. After that, expect to fork out $1,000 to $1,200 per year to store the eggs, Edison says.

The number of eggs harvested depends on the individual, but in general experts recommend putting away 15 to 20. For women younger than 35, sometimes a single cycle will produce that number. A woman closer to 40 may need two to three cycles to produce the number of eggs her doctor has recommended.

Unless you work for Apple or Facebook, the cost of those cycles is likely to come out of your pocket. The majority of people pay with loans or other forms of financing, Edison says. Others use what Angeline Beltsos, the medical director for the Fertility Centers of Illinois, calls “grandparents’ insurance”: Their parents help cover the cost.

Steps in egg freezing

The first step is a consultation, where you’ll probably discuss your ovarian reserve — that is, about how many eggs are available based on your natural fertility.

You might recall from high school sex ed that a woman is born with all of her follicles—the fluid-filled spheres inside which eggs mature. Women have about a million follicles at birth — and that’s it. As a woman ages, her fertility declines. No single test exists to answer with certainty how many eggs are available, but through blood tests or an ultrasound, a doctor can make a pretty good estimate.

You may also discuss more-personal questions, such as: Is having a baby the most important thing to you, or is falling in love and having a baby with a partner more important? For many, egg freezing removes that “I must meet someone and marry and pop out babies” pressure that women may start to feel at some point in their 20s. Taking care of your eggs now means — to some degree — that you don’t have to worry about them in the future, Fino says.

Yet, as about half of the women in the NYU survey reported, there are also emotional drawbacks. “Egg freezing hits a place in our hearts as we contemplate what we want to do with our life,” Beltsos says. “It’s a reminder to some women that they don’t have someone.”

Egg retrieval

The next step is hormone treatment to stimulate egg production. This typically involves oral doses, subcutaneous injections to the abdomen and frequent endocrinologist visits to make sure everything is going smoothly.

During this time, there is a small chance (Fino estimates 1 to 2 percent) of ovarian hyperstimulation syndrome: Because of the extra hormones, the ovaries can become swollen and painful. Often the syndrome resolves on its own, but some people need to be hospitalized.

After 10 to 14 days of hormone treatment, you undergo an egg retrieval procedure, which takes about 30 minutes and requires sedation. A thin needle is inserted into an ultrasound guide, which pierces the vagina and enters the follicles to retrieve the mature eggs. A suction device is used to drain fluid from each follicle and the egg is retrieved. Risks are small, but you may experience soreness for up to a week.

After the eggs are collected, they’re frozen using either a slow-freeze method or a fast-freeze process called vitrification. Freezing is complicated because the eggs have a high water composition, and if ice forms, they’re damaged.

So how do you freeze a watery egg without creating ice? Both methods replace intercellular water with cryoprotectants — chemicals that help prevent ice crystals from forming. Slow-freeze methods, which were more common until recently, introduce cryoprotectants gradually, as the eggs are cooling. Vitrification, on the other hand, uses high initial concentrations of cryoprotectants in combination with faster cooling so that ice crystals don’t have time to form. Because of the reduced risk of ice, some clinics now use this method exclusively.

Frozen eggs are held at sub-zero temperatures at a fertility center or egg bank until you decide to use them. The eggs are good for at least a decade — and probably longer — as long as they are stored correctly, experts say.

And if you move, there are companies that specialize in transporting cryopreserved material — at a cost of around $1,000, according to one company. There’s also risk involved, since something could happen in shipment that makes the eggs unusable.

Maybe baby

Egg freezing doesn’t guarantee the ability to have a baby. “People think frozen eggs are as good as fresh eggs, and that’s not true,” says Kutluk Oktay, an expert in fertility preservation. “When you preserve eggs, you preserve the possibility of getting pregnant.”

While the American Society for Reproductive Medicine says a single thawed egg has a 2 to 12 percent chance of yielding a baby, success rates vary depending on the age at which the eggs were retrieved and the age at which a woman uses them. Both Oktay and Mesen also have online calculators that provide estimates based on data from separate studies.

But just because you freeze eggs doesn’t mean you’ll use them. When you decide to try to have a baby, even if you’re 40 and have a partner or spouse, your doctor may suggest trying naturally for a few months. If that doesn’t work, your doc may recommend IVF using fresh eggs because there’s a finite number of frozen eggs and you may want a second child, Fino explains.

Oktay adds that because elective egg freezing is relatively new, there could be other unknowns. “We are 99.9 percent sure we won’t have any issues with these children. But we need another 10 to 20 years of data to say definitively that all of these children are healthy and don’t have increased problems compared to naturally born babies.”