Hoping to freeze your eggs now so you can get pregnant after you’re well settled into your career 10 years from now? It’s tempting to think of egg freezing as exactly that kind of security deposit on your future—and certainly the plethora of splashy startups and celebrities trying it for themselves make it sound like the smart thing to do. But in reality, spending tens of thousands of dollars doesn’t necessarily guarantee a healthy baby.

“Egg freezing is frequently sold to the general public as an insurance. It’s anything but,” says Norbert Gleicher, MD, the medical director and chief scientist at the Center for Human Reproduction. “When you buy car insurance, you know what to expect if you get into a car accident. But no one can tell a 25-year-old exactly how many eggs she needs to freeze, or her pregnancy chances should she use those eggs.”

The history of egg freezing

Technologies have advanced a lot since the first baby was born from a frozen egg in 1986. Today, vitrification (aka snap freezing) helps prevent ice crystals from forming in frozen eggs, which ensures many more survive the thawing process. “Eggs are the largest cell in the human body, so they have the most cytoplasm, or water. And ice crystals can damage the DNA in an egg,” says Mindy Christianson, M.D., the medical director of the Johns Hopkins Fertility Center, who works mostly with cancer patients who are trying to preserve their fertility. “The technology now has very good outcomes,” she says, with well over 90 percent of embryos surviving the freezing and thawing process.

These improvements led the American Society for Reproductive Medicine (ASRM) to release new guidelines in 2012 stating that egg freezing should no longer be considered experimental. In 2014, the American College of Obstetricians and Gynecologists (ACOG) followed, stating that it was particularly useful to preserve the fertility of people undergoing chemotherapy or people with certain genetic conditions that can affect the quality of their eggs.

“Once the experimental label came off, [egg freezing] really exploded,” says Lynn Westphal, MD, the chief medical officer of Kindbody, a women’s health and fertility clinic that offers egg freezing. Big tech companies like Facebook, Google, and Apple began offering egg freezing as a perk to employees, and some insurance companies began covering some costs. In 2017, there were 10,936 egg freezing cycles, according to the Society for Assisted Reproductive Technology, up from 8,825 in 2016.

Yet the number of babies actually being born via egg freezing is limited—not because the science isn’t there, but because of the limitations of being human. After all, even the most fertile couple in their 20s has just a 20 to 25 percent chance of getting pregnant naturally each month, says Dr. Westphal. This is the side of the story that many experts feel isn’t being adequately communicated to women amidst the popular push to freeze your eggs.

There’s no simple way to tell whether your eggs are “good”

Before starting the egg freezing process, doctors look at a patient’s ovarian reserve (the amount of eggs they have) and their age to answer one important question: How many eggs they need to freeze for the best possible chance of at least one baby. “There’s no magic number,” says Dr. Christianson.

To do this, a person would take a blood test to check their anti-Mullerian hormone (AMH) levels, a hormone released by the ovaries that can give an indication of one’s egg count. An ultrasound then helps doctors count your number of follicles at beginning of your cycle to see if everything looks as expected for your age.

“Patients perceive those eggs as their insurance, but that is not correct. Frozen eggs may give you some additional backup, but how much and how reliably is very difficult to predict.” —Norbert Gleicher, MD, medical director at the Center of Human Reproduction

Freezing a dozen eggs, however, doesn’t mean you’ll have a dozen babies. “At the time we freeze eggs, we don’t know if they’re chromosomally normal or not,” says Dr. Westphal. (Chromosomally normal means that an egg is healthy and functioning with the correct amount of chromosome pairs to create human life if fertilized.) As a person ages, their eggs age with them, and thus the likelihood that some eggs will be abnormal begins to increase in the mid-30s and accelerates quickly in your late 30s. By the age of 40, over half of a woman’s eggs are chromosomally abnormal, says Dr. Christianson. However, you’ll only know if any particular egg is normal until it’s paired with sperm. Many abnormal eggs simply won’t get fertilized; the ones that do often result in embryos that fail to implant or are miscarried.

Plus, as people with uteruses age, they also have fewer eggs. People in their early to mid-30s can expect to get about 10 to 15 eggs per cycle, say experts, and about six to eight by the age of 40. (Of course, those numbers might also not live up to expectations, as one Well+Good writer can attest.)

There’s a good chance you’ll have to do more than one cycle

While a person might go into egg freezing hoping to pay for one cycle and be done, that’s pretty rarely the case.  “In one cycle you’ll not get to a decent chance of having one child,” says Dr. Gleicher. “Very few centers tell you that you’ll likely need more than one cycle.” A 2017 paper found that women at ages 34, 37, or 42 years old would have to freeze 10, 20, and 61 eggs, respectively, to have a 75 percent likelihood of having at least one baby. With somewhere between six to 15 eggs collected at most in a cycle, many people have to go through at least two cycles just to have that three in four chance of delivering a healthy child—and if they want more than one child, they’d need to freeze that many more eggs (and go through that many more cycles).

Egg freezing costs vary depending on where you live but are often in the range of $15,000 to $20,000, including medications, which run about $5,000 per cycle. Most clinics include the first year of storage and freezing costs and then charge a yearly storage fee of $50 to $100 a month. The price is unlikely to decrease much, notes Dr. Westphal, as the cost of medication, surgery, and equipment make up the bulk of expenses, and they’re relatively fixed.

While a few big companies offer egg freezing as a perk to employees, most insurers don’t cover it. “I think as more and more women are aware of egg freezing, they’re asking for it from their employers, so I think it will be increasingly covered as a benefit,” says Dr. Westphal. She adds that the costs are reasonable considering the process involved. “If you go to the ER for tests, you’d probably be paying more than for a cycle of egg freezing,” she says. A 2015 study found that egg freezing before the age of 35 was more cost-effective than IVF over the age of 40, notes Dr. Christianson.

Also keep in mind that those eggs may very well stay in the freezer: A 2018 study of several hundred women who froze their eggs between 2008 and 2017 at two fertility centers in the U.K. found that just a fifth came back to use their thawed eggs. Of those women, only 21 percent ended up getting pregnant, although a quarter of those women still had eggs left to use.

Egg freezing isn’t always treated like a medical procedure

Dr. Gleicher insists that he’s not against social egg freezing outright. Women are having kids at an older age, and egg freezing is an imperfect solution to the issue of declining fertility. However, he’s concerned that the existing fertility industry isn’t being as up-front as it should be about what the process of egg freezing entails—and what reasonable outcomes look like. “There has been considerable outside money from investors pushed into the field, so it’s being sold as a product rather than a medical service,” says Dr. Gleicher. “I consider it inappropriate, unethical, and to some degree even dangerous to induce healthy people into what is clearly a medical procedure without full informed consent.”

“Like anything else in medicine or biology, it is not guaranteed to be successful in the future. We tailor consultations to each patient’s personal goals and their fertility assessment results.” —Joshua U. Klein, MD, chief clinical officer at Extend Fertility

Indeed, his opinion is held by other traditional health organizations. Despite taking the “experimental” label off of egg freezing in general, the ASRM still cautions that “there are not yet sufficient data to recommend oocyte cryopreservation for the sole purpose of circumventing reproductive aging in healthy women because there are no data to support the safety, efficacy, ethics, emotional risks, and cost-effectiveness of oocyte cryopreservation for this indication.”

Certain clinics are taking concerted steps to address those concerns. “It is important for prospective patients to understand success rates and not view egg freezing as an ‘insurance policy.’ Like anything else in medicine or biology, it is not guaranteed to be successful in the future. We tailor consultations to each patient’s personal goals and their fertility assessment results,” says Joshua U. Klein, MD, the co-founder and the chief clinical officer of Extend Fertility, a fertility clinic that specializes in egg freezing. But despite the risks and the varying outcomes, he still stands by social egg freezing. “A woman also might freeze her eggs and never use them [because she has] children naturally or chooses not to have biological children. She has still made a good decision or investment by freezing her eggs as she has preserved her fertility options, allowing her to make choices in her life under less ‘biological clock pressure’ that she might otherwise feel.”

What should you do if you’re concerned about your fertility?

If you’re concerned about your future fertility, experts suggest talking to your OB/GYN about whether you should test your ovarian reserve.

Keep in mind if you do get tested (especially if it’s through a mail-order kit), it’s essential to talk to an expert who can explain your results and what they mean in real life. While AMH levels are pretty good at predicting how many eggs a person has, for example, “they’re not good at telling how fertile a woman is or how likely she is to get pregnant naturally, especially if it’s a younger woman,” says Dr. Westphal.

For people interested in freezing their eggs, the earlier the better (read: before the age of 35). That said, Dr. Christianson generally advises patients to skip egg freezing if they have low ovarian reserve, regardless of eggs. Similarly, Dr. Westphal says that egg freezing probably isn’t a good investment for women who are over the age of 41 or who have very poor ovarian function—although there are always exceptions. “Some young women say that even if I just get a couple of eggs, at least it gives me a small chance. It really depends on how the patient wants to go through knowing the odds are low but not going to get better,” she says.

Dr. Gleicher is more conservative: He generally advises patients in their late 30s that it’s too late to freeze their eggs. “We will be brutally honest about how many eggs we think they can get in single cycle and how many cycles they will have to undergo and the costs,” he says.

None of this is to dismiss egg freezing’s potential or to scare people off from it. But the experts we spoke to want people to understand that egg freezing, like any other fertility-related treatment, is a medical procedure that comes with its own share of risks and a difficult-to-predict set of outcomes. “Patients perceive those eggs as their insurance, but that is not correct. Frozen eggs may give you some additional backup, but how much and how reliably is very difficult to predict,” Dr. Gleicher says. Ultimately, knowing that there are no certain outcomes needs to be a part of the conversation, too.

Is fertility genetic? Kind of—and kind of not. But men certainly should be part of the conversation, too.