Mobile devices are teaching modern women something their ancient counterparts knew thousands of years ago: How to track fertility.

This may seem like a niche opportunity, but a sizable chunk of the U.S. population suffers from fertility issues. According to the Centers for Disease Control and Prevention, 6.7 million women in the U.S. struggle with infertility, representing 10.9 percent of women aged 15 to 44.

About one-third of these cases is diagnosed as “unexplained infertility,” meaning that doctors can find no underlying cause from diagnostic testing.

Over the past fifty years, the medical community has developed an arsenal of methods to overcome reproductive hurdles. Women can choose to freeze their eggs, take fertility drugs, get artificially inseminated, use a surrogate, or undergo in vitro fertilization (IVF) -- all options that cost tens, or even hundreds of thousands, of dollars.

However, when a woman struggles to conceive, a gap exists between the “keep trying” strategy and the decision to shell out a year’s salary or more for fertility treatments.

A new crop of fertility startups are working to bridge the gap.

“There is not much in the middle between doing nothing and undergoing assistive reproductive treatments, which can be quite invasive and stressful," said Will Sacks, cofounder and chief executive of a mobile app called Kindara Health.

Kindara, along with fellow fertility startups, are leveraging mobile devices, connected hardware and reproductive science to help women take their fertility into their own hands.

Kindara’s mobile product is based on "Fertility Awareness Methods" where women chart their primary fertility signs to gauge what time of the month they are most fertile. Based on that data, Kindara provides charts that show women where they are in their cycle and their corresponding fertility levels.

In addition to the app, Kindara recently released a connected fertility thermometer called Wink that reads basal body temperature and automatically syncs that data to the app.

Sacks said Kindara’s overarching goal is to help women better understand their reproductive health, whether or not they are trying to get pregnant.

“The cultural messaging to women is that your body is owned partially by the state, partially by God, and it is a scary black box that it is best to ignore or stay away from,” Sacks said. “As a result, so many women never really have a relationship with their cycle or understand it.”

Can These Apps Help Women Get Pregnant?

Sacks founded Kindara with his girlfriend Kati Bicknell after the couple began practicing fertility awareness as an alternative to conventional birth control methods.

They realized there was a serious lack of available information about fertility awareness and wanted to build a company that made it easier to learn about and adhere to. While their initial interest was in tracking physiological signs as a form of birth control, 60 percent of women using Kindara are trying to get pregnant. According to Sacks, the app has helped over 60,000 women get pregnant since its launch two years ago.

Unlike Sacks, who admittedly knew nothing about fertility until somewhat recently, Kirsten Hurder-Karchmer had 15 years of experience running one of the largest fertility wellness clinics in North America before founding her fertility startup, Conceivable. Austin, Texas-based Hurder-Karchmer is a reproductive acupuncturist who specializes in integrating Eastern and Western medicine to improve reproductive health.

Conceivable offers a version of her fertility program that is delivered via a mobile app. It addresses three key areas: Menstrual cycle, lifestyle, and mindfulness -- all based on the findings of dozens of studies from peer-reviewed journals.

“Lifestyle matters more than people think when it comes to getting pregnant,” Hurder-Karchmer said. “Diet, water consumption, weight, how active you are, your alcohol and tobacco use -- all these factors affect your fertility."

A team of Harvard researchers found that replacing animal sources of protein with vegetable sources of protein can reduce the risk of ovulatory infertility. A study from Hopkins found that women who are attempting to conceive should abstain from consuming alcohol. And NIH researchers discovered that stress significantly reduces the probability of conception.

The Conceivable app uses these findings and many others to help women adopt a lifestyle that optimizes their fertility. The app provides veggie-centric meal plans and recipes; helps regulate daily consumption of water, soda, and alcoholic drinks; tracks sleeping patterns and exercise; and promotes therapeutic practices to help reduce stress and anxiety.

Participants in the program also receive three distinct herbal remedies a month. The herbal approach has drawn plenty of skepticism from devotees of Western medicine, but there are some recent studies that suggest it can help.

Loriana Aldama, who recently tried out Conceivable, said she got pregnant in seven months, after trying IVF twice. Her fertility doctor had told her that her chances were "slim to nothing."

Fertility Tracking Apps are a Big Trend

There has been a veritable flowering of fertility tracking apps over the past couple years.

Other well-known apps in the space include Clue, Ovia Fertility, Fertility Friend, Lily, and Glow, to name a few. Glow rocketed this sector into the spotlight after its founder -- well-known entrepreneur and PayPal cofounder Max Levchin -- unveiled Glow at the AllThingsD (now Recode) conference, where he created a stir by discussing  “cervical mucus” on stage.

But Clue founder Ida Tin said that while interest in this space is exciting, there is still a long way to go.

“I think we have a menstruation revolution going on and it is all coming from startups,” Tin said.

“No big players in the field have taken this completely foundational part of human life and turned it into a really serious grown up digital product. Female health has been so under-served, even though it is one of the biggest areas for spending in the health industry.”

Rather than tracking basal body temperature and cervical mucus -- like Kindara, Ovia, and Glow -- Clue uses the calendar method, which forecasts fertility based on your last period’s start and end dates, as well as additional information like mood or cramps.

Each of these apps functions by collecting intimate, highly personal data, which raises questions about privacy.

Advertisers are already targeting consumers with offers based on their purchasing behavior. Back in 2012, Target set off a firestorm when it figured out that a teen girl was pregnant based on her purchases -- before her father knew -- and sent her pregnancy and baby-related coupons in the mail. Data from these fertility apps would take those capabilities to a whole new level. Or what if an employer was able to access that data to discover if an employee was pregnant or trying to be? That information could affect hiring, promotion, or salary decisions.

However, Kindara user Abby Winship Hoyes said that the benefits of using the app outweighs her privacy concerns.

“I am aware of the potential privacy concerns, but frankly, they never bothered me,” she said.

“As far as I'm concerned, if someone wants to troll through my often inconsistent and sometimes inaccurate data, more power to them. I should hope that I wouldn't suffer any discrimination based on what this data says about me.”

Ancient Wisdom in a Mobile App?

Each of these startups is essentially channeling ancient wisdom about fertility into the form of a mobile app. The apps are using new technology to resurrect decidedly low-tech fertility practices that existed thousands of years before IVF, smartphones, or gynecologists.

While these mobile apps are certainly helping to provide women with more options, Dr. Richard Paulson said it is important to remember there is only so much they can do. Dr. Paulson is the President Elect of the American Society for Reproductive Medicine and a professor of reproductive medicine at the University of Southern California.

“In my mind, mobile apps fit in right at the beginning by helping people making sure the woman has regular ovulation and that they are having sex at the correct time," he said.

If there is some impediment preventing someone from getting pregnant, the apps won’t help, said Paulson. And more specialized treatments like IVF may become simpler, cheaper and less expensive.

Fertility is a spectrum. Most women are not exclusively fertile or infertile -- their fertility fluctuates depending on a complicated interplay of factors.

These mobile apps take varied, but similar approaches to helping women understand these fluctuations and empowering them to take their fertility into their own hands. However, if there are physiological impediments to getting pregnant -- such as endometriosis or blocked fallopian tubes -- a mobile app can only play a limited role in overcoming them.

What they can help women overcome are social stigmas that keep them removed from their own reproductive health. We still live in a society where a modest image of period blood is considered obscene. For the millions of women with“unexplained infertility,” those social impediments can be the tallest.