CAMBRIDGE, Mass. — Gilbert Sanchez froze his sperm in January, shortly before his 25th birthday. He was healthy and at low-risk for fertility issues. But he wanted to be proactive — just as thousands of young women have been by putting their eggs on ice.

Sanchez was headed to graduate school in the fall, and it might be years before he would have a steady job and the wherewithal for a family. He and his girlfriend worried about all the things that could go wrong — disease, war, natural aging — before they might be ready.

"It was a little bit weird," admitted Sanchez, who stored his sperm with a company called Legacy. "But it was medically responsible."

Sanchez's choice highlights a new anxiety about sperm health among American men. The idea that men can easily father healthy children into their 70s and 80s has been exposed as a myth. In fact, research shows that older men have a higher risk that their partners will miscarry and have children with congenital abnormalities, schizophrenia or autism.

New businesses are capitalizing on those revelations. Start-ups like Trak, YO sperm and SpermCheck are selling at-home testing kits so men can figure out early on if there's something amiss with their sperm. Employee benefits companies are debating how to translate the fertility coverage they offer to female employees to their male counterparts. And sperm freezing companies are aiming to turn what has been a sterile, clinical process into something more coo — a 23andme or Ancestry.com for sperm.

Legacy, a company based at the Harvard Innovation Labs that launched in October, is part of a new breed of sperm freezing companies that aim to shake up the industry by offering mail-in kits that allow the whole process to be done in the privacy of one's home. A competitor, called Dadi (pronounced "daddy") and backed by $2 million in venture capital from New York and Silicon Valley, launched at the end of January.

Their message is that sperm freezing shouldn't just be for men suffering from infertility, cancer or heading off to a war zone — but something every male should consider.

"I view this as an insurance policy for the future," said Legacy's CEO, Khaled Kteily. Kteily, who recently turned 30, was his company's first client.

Tom Smith, Dadi's chief executive, argued that "men have a biological clock just like women. This gives them the option to start a family when the time is right for them."

Part of these companies' sales pitch is that, at a population level, sperm quality appears to have fallen precipitously at all ages for reasons we don't yet understand. That headline-grabbing finding, published in a 2017 study, triggered widespread debate about its implications. But many fertility specialists see little cause for immediate alarm. Despite the decline, the average male still produces several million sperm cells each day — more than enough to produce his progeny and keep the human race going many times over.

As such, some believe sperm freezing for the masses is overkill.

Tracey Woodruff, who directs the Program on Reproductive Health and the Environment at University of California at San Francisco, believes concerns about male infertility should be focused on preventing the issues in the first place — for instance, with stronger regulations of substances affecting male reproduction.

Natan Bar-Chama, a male infertility specialist at Reproductive Medicine Associates of New York, said tracking sperm quality can be useful for general health reasons. Research shows that semen abnormalities — similar to those found in blood — can serve as an indicator of hormone, circulatory, urinary and skin conditions. But because men's sperm quality does not deteriorate with age nearly as sharply as women's egg quality, Bar-Chama said, they have more time to make important life decisions making sperm freezing unnecessary for most men.

"A normal healthy male in his 20s and 30s — we don't recommend it," Bar-Chama said. "If we're talking about someone in his 40s, who thinks he is not going to have children until he is in his 60s, it's up for discussion. There isn't the same urgency as there is for freezing eggs."

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Women have been the focus of IVF treatment marketing, talk about the "fertility cliff" and pregnancy troubles for so long that it's easy to forget the men. The reality is that male factors are at play in 30 to 50 percent of cases of couples having trouble getting pregnant — and nearly all those cases are related to sperm.

But there are huge differences between how eggs and sperm age.

Women's eggs are believed to be finite in quantity, with the average woman having 1 million to 2 million eggs at birth and then releasing some of those eggs each month starting in adolescence. Men, by contrast, replenish their supply of sperm at a rate of about 1,500 sperm per second — or several million each day.

While the impact of lifestyle factors on egg quality is still being studied, it's widely accepted that sperm characteristics can fluctuate by the month or perhaps even day, based on a man's health, habits, and environment.

One study, based in Denmark and published in 2010, found that men's sperm was slightly reduced in those who drank a lot of soda or caffeine. Others have found that television watching, cycling and spending time in hot tubs may also impact sperm quality. The U.S. Environmental Protection Agency has said there's moderate evidence that types of phthalates — a chemical used in the production of consumer products such as shoes, garden hoses and paint — may impact male reproduction.

When assessing sperm, doctors look at three main measures — concentration, motility and morphology. Concentration refers to the number of sperm per unit of semen. At least 15 million sperm per milliliter is considered good. Motility is about how sperm move, which will determine whether they are able to swim through a woman's cervix, into her uterus and fallopian tubes to reach the eggs. Morphology refers to the shape and structure of the sperm.

Men with issues related to sperm concentration, motility or morphology may have trouble getting their partners pregnant.

Fortunately, they have an easily available, albeit expensive, medical option called ICSI — or intracytoplasmic sperm injection — a procedure invented in 1987 that involves taking a single sperm and injecting it directly into an egg as part of in vitro fertilization. If a man can produce any sperm at all, which all but very few men can do, doctors say they should be able to have biological children through this procedure.

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Daniel Madero is Legacy's head of clinic partnerships. His father is a fertility specialist in Colombia and said that when he first had his sperm count done 12 years ago at age 19, it looked great — "it was in the millions and the motility it was ahh-mazing." He and his friends joke that it was the "Usain Bolt of sperm," the "Michael Phelps of sperm."

His numbers have plummeted by almost half since then.

Madero and his wife, who have been married for two years, aren't ready to have children so Madero froze his sperm, and they are talking about her freezing her eggs as well.

But egg freezing and sperm freezing involve wildly different risks and expenses.

Egg freezing involves an invasive, multiweek process of hormone injections and a surgical procedure that can cost $10,000 to $15,000. It usually yields anywhere from a half-dozen to a dozen eggs. Sperm freezing is much simpler and less expensive. Under Legacy's service, a man would order a kit online and put a sample into the container, mix it with a preservative and mail it back to the company. The sample — which would typically contain millions of sperm — would be tested, and a report sent back to the customer evaluating the health of the sperm.

Data security and privacy are a key part of Legacy's pitch. The company is based in Europe, because of the continent's stronger privacy laws, as compared to the United States. Clients are assigned a number — like a Swiss bank account — that is used to label the samples and communicate with the company. Everything is encrypted, Kteily said, and the company does not sell its data.

The lab then splits the semen into different "straws" to be stored in two separate cryotanks in two separate locations in the United States. Kteily says all the labs they work with, which he won't reveal for privacy reasons, are licensed by the Food and Drug Administration. Dadi uses one storage facility that is FDA licensed.

The cost of sperm freezing can vary a great deal. If you do it in a fertility center, it can sometimes run you over $1,000 for the collection and testing. Legacy's mail-in packages start at $350 for one "deposit" and $20 per month for storage. Dadi uses one storage facility but its cost is significantly cheaper — an initial $99 fee for the collection kit and test, plus $9.99 a month or $99 annually for storage.

Legacy and Dadi declined to reveal the number of sales so far, but Legacy said clients are from all across the United States. They are typically aged 30s to 40s with Sanchez, a project manager from Phoenix, among the youngest. Many have stories like Rami, a 26-year-old who works in the tech industry in San Francisco, and who asked that his last name not be used, "so if you Google me the first thing you get won't be about sperm." Rami said he decided to freeze his sperm earlier this year because of his older friends' struggles with infertility.

"I knew the pain they went through," Rami said.

Meanwhile, many women — wives, girlfriends, sisters, mothers — have seized on sperm freezing as a sign of reproductive equality.

"It makes the discussion more complete," said Anna Barnacka, 35, chief executive of a Boston-area company. "Male and females both have issues with fertility. It's not just one side."