Washington - Like millions of women, Diana Diller was a devoted user of the pregnancy-tracking app Ovia, logging in every night to record new details on a screen asking about her bodily functions, sex drive, medications and mood.
When she gave birth last year, she used the app to chart her baby's first online medical data - including her name, her location, and whether there had been any complications - before leaving the hospital's recovery room.
But someone else was regularly checking in, too: her employer, which paid to gain access to the intimate details of its workers' personal lives, from their trying-to-conceive months to early motherhood.
Diller's bosses could look up aggregate data on how many workers using Ovia's fertility, pregnancy and parenting apps had faced high-risk pregnancies or gave birth prematurely; the top medical questions they had researched; and how soon they had returned to work.
"Maybe I'm naive, but I thought of it as positive reinforcement: They're trying to help me take care of myself," said Diller, 39, an event planner in Los Angeles for the videogame company Activision Blizzard. The decision to track her pregnancy had been made easier by the $1 a day in gift cards the company paid her to use the app: That's "diaper and formula money," she said.
Period- and pregnancy-tracking apps such as Ovia have climbed in popularity as fun, friendly companions for the daunting uncertainties of childbirth, and many expectant women check in daily to see, for instance, how their unborn baby's size compares to different fruits or Parisian desserts.
But Ovia also has become a powerful monitoring tool for employers and health insurers, which under the banner of corporate wellness have aggressively pushed to gather more data about their workers' lives than ever before.
Emboldened by the popularity of Fitbits and other tracking technologies, Ovia has marketed itself as shepherding one of the oldest milestones in human existence into the digital age.
By giving counseling and feedback on mothers' progress, executives said, Ovia has helped women conceive after months of infertility and even saved the lives of women who wouldn't otherwise have realized they were at risk.
But health and privacy advocates say this new generation of "menstrual surveillance" tools is pushing the limits of what women will share about one of the most sensitive moments of their lives.
The apps, they say, are designed largely to benefit not the women but their employers and insurers, who gain a sweeping new benchmark on which to assess their workers as they consider the next steps for their families and careers.
"What could possibly be the most optimistic, best-faith reason for an employer to know how many high-risk pregnancies their employees have? So they can put more brochures in the break room?" asked Karen Levy, a Cornell University assistant professor who has researched family and workplace monitoring.
"The real benefit of self-tracking is always to the company," Levy said. "People are being asked to do this at a time when they're incredibly vulnerable and may not have any sense where that data is being passed."
The rise of pregnancy-tracking apps shows how some companies increasingly view the human body as a technological gold mine, rich with a vast range of health data their algorithms can track and analyze.
Companies pay for Ovia's "family benefits solution" package on a per-employee basis, but Ovia also makes money off targeted in-app advertising, including from sellers of fertility-support supplements, life insurance, cord-blood banking and cleaning products.