text: If you browse HealthKit, Apple's health-tracking app, you might think that its female users don't menstruate.
  
  The app, after all, includes dozens of metrics like blood type, body temperature and exercise, but not a single way to track one's period.
  
  When HealthKit debuted in the spring, critics quickly pointed out this oversight as yet another example of how the male-dominated tech industry can't see beyond its own experiences.
  
  Apple finally remedied the omission on Monday at its annual Worldwide Developers Conference by announcing the inclusion of reproductive health in an upcoming version of the app. While Apple hasn't provided more details on its features, the change is a welcome improvement, and one that many users are likely to enjoy.
  
  Hydration, UV exposure, and REPRODUCTIVE HEALTH added to Health. Period/fertility trackers? TODAY IS LADY POWERRR #Apple #WWDC
  
  — Xeni Jardin (@xeni) June 8, 2015
  
  Period trackers are in fact very popular. Women commonly use them to boost their chances of getting pregnant, though others use them as a contraception aid. Either way, collecting data about one's period can provide a woman with powerful information.
  
  Organizing this data digitally, and analyzing it alongside other health metrics, may eventually provide patients and doctors with a comprehensive picture of their reproductive health.
  
  Trackers help solve a simple problem, which is that a woman's cycle can be unpredictable and difficult to recount from memory. Dr. Nathaniel G. DeNicola, who practices obstetrics and gynecology at the University of Pennsylvania Health System, says that a menstrual cycle can be anywhere from 21 to 35 days long and can fluctuate depending on the type of contraception she's using.
  
  DeNicola, also a senior fellow at the Penn Social Media and Health Innovation Lab, tells Mashable that one of the most important vital signs for his patients is the date of their last period, which can help determine a due date.
  
  "More and more women pull out their phone," he says.
  
  There's no evidence to show that using a tracking app leads to improved predictions for due dates, but DeNicola says it can be a more reliable tool than a pen and paper.
  
  He also warns patients against believing claims that apps are a proven form of birth control when used to track a woman's fertility. The so-called rhythm method, which uses temperature and other factors to gauge fertility, has a 25% failure rate, and DeNicola says no app can dramatically improve those odds.
  
  Hans Raffauf, chief operating officer for the reproductive health app Clue, says he is excited for the possibility of pulling dozens of metrics from Apple's app to consider alongside menstruation data. "If a woman is an active runner, does that have an affect on her cycle we can measure?" says Raffauf.
  
  Only access to large amounts of data would help Clue answer this and similar questions, but Raffauf sees the potential.
  
  The potential for revenue is also considerable. Clue's own market research shows that period and pregnancy tracking apps are the second-largest by sales among health apps. Clue, according to Raffauf, is downloaded an average of 10,000 times a day.
  
  Period tracking, though, isn't just about fertility. Specific information about a woman's cycle can help a physician make a diagnosis or evaluate treatment for endometriosis, a condition that affects the tissue lining the uterus. And if a post-menopausal woman experiences bleeding and tracks those symptoms, it can alert her doctor to the possibility of uterine cancer.
  
  DeNicola welcomed the addition of reproductive health to HealthKit, saying that no field would want to be left out of the phenomenon of patient-generated data.
  
  DeNicola says that the more patients and doctors use these apps, the more they'll reflect the unique needs of women.
  
  "Inevitably," he says, "there will be things we haven’t thought of yet."
  
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summary: Apple finally remedied a big omission on its HealthKit app.