Jennifer Hayes had always wanted a child. And like many other American women, Hayes figured she would have at least one by the time she reached her early 30s. But when she hit her 34th birthday in 2009, she was unmarried, childless, and spending long hours battling to keep her Telluride restaurant business afloat amid the recession. “I had a baby shower to go to every other weekend, and I felt like the only person in my world who wasn’t married,” Hayes says. “I was really, really tired of worrying about my biological clock.”

Not too long thereafter, Hayes learned that there might be a way to silence the ticking. A friend who, at the age of 40, was undergoing in vitro fertilization (IVF) at a Denver clinic told Hayes about a new procedure designed to preserve women’s fertility. She urged Hayes to look into it. Do anything you can, she said, to avoid the stressful and costly multiple IVF rounds she and her husband were experiencing.

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The following year, Hayes traveled from Telluride to the Colorado Center for Reproductive Medicine (CCRM) in Lone Tree. It was there that Hayes decided to move forward with something called oocyte cryopreservation. Within six weeks, the now 37-year-old had 19 eggs cradled in a cryogenic tank, indefinitely suspended in time.

Like Jennifer Hayes, more and more Americans are waiting longer and longer to marry and start families. In fact, the median age for an American woman to get married for the first time is 26—up from 22 in 1980—and the average age at which she has her first child has risen to 25 from 21 in 1970. Those statistics mean that some American women are seriously pushing the outer limits of normal human fertility.

As such, women are turning to technology to nudge those boundaries outward. The emerging field of oocyte cryopreservation—or egg freezing—is one of the newest methods through which women are hoping to preserve their ability to have a biological child beyond what are considered typical child-bearing years.

Scientists began freezing embryos in the ’80s, but unfertilized eggs, which contain large amounts of liquid prone to viability-destroying crystallization, proved trickier. In 2004, embryologists began experimenting with a new flash-freezing method called vitrification that yielded better results. In the past three years, peer-reviewed studies have illustrated a dramatic change: Before 2007, fewer than a dozen live births from frozen eggs were reported; since then, more than 1,500 babies have been born from frozen eggs worldwide. A literature review by the co-founder of New York University School of Medicine’s Fertility Center reported that babies born from frozen eggs had the same rate of congenital abnormalities as naturally conceived infants, and clinics such as Denver’s CCRM and the NYU center report pregnancy rates for frozen eggs that are similar to those for “fresh” eggs used in traditional IVF.

This technology—and the recent successes it’s had—is ushering in a new era of choice for American women, similar to the one unleashed by the birth control pill in the 1960s. Birth control separated sex and conception to create sexual freedom. But that freedom had certain consequences, of which one was a major uptick in age-related infertility. Egg freezing—at least to some degree—separates fertility from the proverbial biological clock, increasing women’s ability to choose when, how, and with whom to have children.

Dr. William Schoolcraft, founder and medical director of the CCRM, started using the new vitrification method five years ago. Once he added the procedure to his already nationally and internationally known fertility practice, word spread quickly. The number of patients coming to his Lone Tree clinic (there are three CCRM clinics in the metro Denver area) for the process has doubled each of the last three years, rising from 21 in 2010 to 49 in 2011 to a projected 75 to 100 in 2012. Currently, roughly half of Schoolcraft’s clients are freezing their eggs before undergoing treatments like chemotherapy (known to harm the reproductive system), but Schoolcraft expects the number of healthy clients who come simply for fertility preservation to quickly surpass that percentage.

“Traditionally, if women waited until their late-30s or 40s it was too late and the only option was to find a donor egg. This way, they can act as their own donor,” says Schoolcraft, who began freezing embryos at UCLA during his residency in the early 1980s and decided to dedicate his career to solving infertility. “It’s exciting for me because I talk to 42-year-olds who just got married last year and frequently I have to tell them they’re past the point of getting pregnant,” he explains. “They say they wish they’d known about this technology five years ago.”

That may be the case, but the process isn’t truly accessible to everyone and it doesn’t serve as a guarantee that a woman will have a successful pregnancy. Egg freezing is extremely expensive, costing between $10,000 and $20,000. And the process is still considered experimental by the American Society for Reproductive Medicine (ASRM), although that designation dates to 2006 and is under review. “There’s so much research being done in the field, and as more data becomes available that status might change,” says Dr. Samantha Pfeifer, chair of ASRM’s practice committee and associate professor of obstetrics and gynecology at the University of Pennsylvania.

Although Schoolcraft is confident in his roughly 60 percent success rate (comparable to his IVF rates) and pleased with the 50 live births he’s produced using the egg-freezing technology since 2009, he tells patients there are no assurances and describes the egg-freezing procedure as an insurance policy or backup plan. “No one’s saying not to try to get pregnant conventionally; it’s just one more opportunity that women who don’t freeze their own eggs wouldn’t have,” he says.

According to the experts, too many women don’t understand fertility until they learn they no longer have it. ASRM’s Pfeifer says it’s common for patients in their mid- and even late-40s to blithely assume they can get pregnant, merely because they feel young and healthy. “It doesn’t work that way,” she says. Many women who are freezing their eggs say they wish they’d realized earlier how big a role age plays in the ability to conceive, instead of looking to movie stars having babies in their 40s—often through donor eggs—to guide their sense of what’s possible. “Thirty is the new 20 and our whole lives are being pushed back,” says Brigitte Adams, a San Francisco marketing consultant who came to Denver to freeze her eggs at the age of 39. “We think because we’re looking younger and living longer that our window of fertility would be extended, too. But it isn’t.”

One of CCRM’s patients, Renée,* a Denverite who works in financial reporting, was surprised to learn that even at 33, she would have a difficult time conceiving naturally. Recently divorced, she’d elected to freeze her eggs to eliminate “the pressure of having to find somebody and immediately have a baby.” When clinic physicians tested her hormone levels, they found they were similar to those of a woman in her mid-40s. They also discovered that she had a lower-than-normal resting follicle count (number of eggs) for someone her age. Neither problem had been detected during her annual gynecologic exams, as those visits don’t typically include such tests. Six months and $20,000 later, Renée had 21 eggs frozen in storage. Had she waited to find a mate and to conceive naturally, having a child would likely have become even more difficult and more expensive.

While Renée paid her own egg-freezing bill, many patients have help. Hayes’ family assisted her with the medical payments, while Adams’ parents chipped in around $7,000, which paid for half. “It was a family decision because they know how much I want children and they want that to happen for me,” says Hayes, who points out that compared to adoption, egg freezing with the required subsequent IVF process to fertilize the egg and implant the embryo is generally less expensive—and less complicated. “No one questions parents paying for a wedding; why would they question this?”

In addition to the financial commitment, oocyte vitrification entails a physical dedication that varies in intensity. All oocyte vitrification patients must inject themselves with hormones daily for an average of 10 days to stimulate egg maturation. After that, patients are sedated for about 15 minutes while the eggs are harvested in a minimally invasive procedure. But the length of the process and how many cycles it requires depends on each woman’s fertility factors. Hayes’ process lasted six weeks, while Renée’s lasted six months.

Hayes says she realizes that her frozen eggs don’t come with a certificate that reads, “Congrats on your future arrival.” She knows there is no guarantee. But she feels relieved that she’s done everything she can to sustain her dream of motherhood. “What I care about,” she says, “is that I won’t have any regrets.”