When it comes to menstrual cycle-tracking apps, there are three types: Period-tracking, fertility, and contraception. The stakes of the app getting predictions wrong vary by each distinction: You could ruin a pair of underwear, miss your fertility window that month, or accidentally end up pregnant, respectively.
Some popular options say they cover multiple uses. Clue, for example, is both a menstrual cycle and ovulation app, meaning it predicts both the days you’ll bleed as well as your “fertile window,” or when you’re most likely to get pregnant. But before people can start effectively using an app for something like ovulation tracking, they really need to know their cycle.
Often these apps have handy charts that give you the average length of your cycle and period. The average cycle length is 28 days, but regular cycles fall between 21 and 35 days. Changes in weight, exercise routines, and stress can all affect cycles, too. What’s worse, between nine and 14% of the menstruating population have irregular cycles, which can be caused by health issues like polycystic ovary syndrome (PCOS).
“These apps are unfortunately completely not helpful for those patient populations,” Dr. Ann Peters, a surgeon at the Gynecologic Specialty Group at Mercy Medical Center, told Digital Trends.
Having a cycle length longer or shorter than the 21-to-35-day window is the medical definition of an irregular period. But those whose cycles last 27 days one month and 29 the next probably don’t consider it all that regular. Some apps take your historic data into account when showing you when your next period will occur, but these are still just predictions.
“Predicting the precise regularity of it, for each individual woman — it’s virtually impossible,” Dr. Nathaniel DeNicola, an OB-GYN and the chair of telehealth for the American College of Obstetricians and Gynecologists, said.
“… We now have data sets that are so much bigger than what we ever had before.”
The start of your period has pretty obvious signs, but tracking ovulation is trickier. Changes in cervical mucus and a slight rise in body temperature occur, and there are hormonal indications as well. They’re all parts of the fertility awareness method, long used to both prevent pregnancy and conceive. Apps help do the math for you, running proprietary algorithms they often don’t explain.
Doing this method purely by the numbers is risky, as a study from 2000 found only 30% of the 221 participants had a fertile window that fell between 10 and 17 days, the expected average. When an app displays your predicted ovulation span, it’s going to fudge a little before and after, because of the viability of the sperm (up to five days) and egg (about one day). It would make sense for a fertility app to put the emphasis on the days before it predicts you’ll ovulate — since you’re trying to get pregnant — versus a contraceptive app, that would want to ensure you don’t conceive if the algorithm pegs the day wrong.
These apps claim their algorithms get more accurate the more information you input. Logging your acne, sexual encounters, bowel movements — they want all the details. If you divulge everything, you’re giving up information even your best friend might consider too much. Even your doctor may not need to know it all, outside the regularity of your cycle.
“I’m not sure that adding all of that information, from a physician’s perspective, adds a lot of help to our field and our counseling for patients,” Peters said.
In exchange for the data, the apps promise to help you get pregnant, or not, or maybe just give you a heads up that you always get cramps on the second day of your period. As if you didn’t know already.
But apps like Clue are also partnering with researchers, offering hope that women’s health — long understudied — might benefit.
“It’s kind of a new era for doing research in females because we now have data sets that are so much bigger than what we ever had before,” Ida Tin, co-founder and CEO of Clue, said. “And we can collect data so much faster.”
Research projects using Clue’s data include studies around the connection between menstruation and global warming, and the length of adolescents’ periods.
There’s a less altruistic side to the data collection, though. Employers like Activision Blizzard paid employees to use fertility tracker Ovia, according to the Washington Post. The video game maker had access to anonymized data about the number of people working for them who were trying to get pregnant. Another app, Flo, was sharing weight and cycle data with Facebook. Jennifer King, director of Privacy at Stanford’s Center for Internet and Society, warns that anonymized data doesn’t always stay unidentifiable.
“For the most part, if you can pick one or two things that truly identify you, like age and zip code and maybe one more thing, it often doesn’t become that hard to re-identify whatever other data that you’re contributing,” she said.
“Now we are at a point where one could actually monetize your cycle.”
Marketers are also taking an interest in this data. Kristina Durante, an associate professor of marketing at Rutgers Business School, has studied how hormones like estrogen and progesterone might influence what products you buy. She’s consulted with brands about partnering with fertility apps to send marketing messages based on where users are in their cycle.
“When estrogen is high, [women] want to look good, and so they might be more interested in consumer products like lipstick or cosmetics or procedures that help them enhance their appearance,” Durante said.
When the progesterone kicks in, the advertisements might switch to candles or pillows, products associated more with nesting.
“We’re vulnerable at that point,” King said.
When King studied pregnancy apps 10 years ago, they weren’t nearly as sophisticated. They were mostly made by men, she said, not backed by large companies. At the time, she wasn’t quite sure how the data could be used.
“Now we are at a point where one could actually monetize your cycle,” she said. “It’s hard for us to course-correct for anything we don’t know about.”
But knowing brands might soon target you based on your biology could at least make you wary the next time you see an ad for lipstick or linens.
“Everybody assumes that we’re still in — I’ll call it like Internet 2.0 advertising world,” King said. “Where, ‘Oh, they’re just going to show me ads and I can decide if I want to buy that thing or not.”
But by tapping into people’s cycle data, King said it’s based on “something they know about you, and that’s the thing that really creeps people out.”
A recent study found people were using apps not intended for contraception as a form of birth control. Who can blame them? They’re all swimming around the app stores, and many surface whether you search for birth control, fertility, or period-tracking.
“It’s not because they’re stupid to use the app like that, because people have a real need and for many many reasons the birth control that they have access to is not what they want or what they need,” Tin said.
“Women really do want a form of birth control that’s more efficient and protects them the most.”
She said Clue is working on some changes to the app in anticipation of European Union regulatory changes to medical devices and software next year. People look to the fertility window on these apps for guidance, and Tin said she takes that responsibility seriously.
“The last thing we want is to get people unwanted pregnancies,” she said. “That’s huge. I’ve tried that myself. It’s really not fun.”
It’s easy to see why people would want to use these apps, though. Free, non-hormonal birth control appeals to a lot of people. But as Peters points out, the most reliable form of contraception is the kind that’s entirely hands-off.
“Women really do want a form of birth control that’s more efficient and protects them the most,” Peters said. “Generally the ones where they don’t have to do anything are the ones that are going to be the best.”
When the Food and Drug Administration approved the Natural Cycles app as a contraceptive last year, a doctor said in its press release that “women should know that no form of contraception works perfectly, so an unplanned pregnancy could still result from correct usage of this device.” Despite its clearance from the FDA and EU regulators, the app was investigated when 37 Swedish users reported becoming unexpectedly pregnant while using the app as contraception.
Natural Cycles is meant to be used in conjunction with a thermometer that measures the rise in basal body temperature. This is common practice for those trying to conceive, but it’s as easy to forget as taking a pill. Indeed, a study of over 4,000 participants using the app found that user error was the most common reason for becoming pregnant. Thirty-three% of all participants admitted to skipping using protection sometimes or always on “red” days when the app told them they may be ovulating. Ten people became pregnant on “green” days when the app said they should be in the clear to not use protection.
“If you want to be quite precise and scientific (as some journals insist), you would need to have a surgical probe with a camera in the abdominal cavity and see the egg being extruded at the midcycle to have firm ‘evidence of ovulation,’” Dr. Jerilynn Prior, founder of the Centre for Menstrual Cycle and Ovulation Research, told Digital Trends in an email.
Both Peters and DeNicola have had many patients whip out an app during an appointment. This is how DeNicola would prefer to have people use them, with input from their physician.
“It still raises issues with like, ‘Who are these people? What are they doing with my data?’”
“None of the algorithms have been tested enough that we can confidently say that the risk of pregnancy, if they’re using it for contraception, has changed,” DeNicola said. “So if people are using it to try to avoid pregnancy they should still be in the same counseling as anybody would be using if they’re doing it without an app.”
When people have fertility issues, they’re generally advised to wait six months to a year, depending on their age, before seeing a doctor. During that interim, these apps give “patients some control over the process,” Peters said.
“Much of the time it might be either neutral or even add some value but in the cases where it could be risky, it’ll be good to have doctors input,” DeNicola said.
If someone with fertility issues were to solely rely on an app, who’s to say it couldn’t start nudging them toward in vitro a few months before they really need to consider it — especially if the app partnered with a clinic offering those services.
After looking at thousands of reviews for cycle-tracking apps and conducting hundreds of interviews, a University of Washington research team found common complaints, like an inability to correct errors in cycle predictions; cutesy, pink designs; and a lock on user data that wouldn’t allow them to export it to other apps and trackers.
Some apps won’t allow you to chart periods that are longer or shorter than the average two to seven days. In 2016, researchers looked at 108 apps and found only 20 were accurate. Barely any — only 5% — cited medical literature or professional relationships.
“It’s kind of like trying to regulate the internet,” DeNicola said.
King said there are still a lot of apps that have been made by individuals instead of professional organizations.
“It still raises issues with like, ‘Who are these people? What are they doing with my data?’” she said.
These apps have a lot to offer, but they’re also asking for a lot in return. You have to choose the right type of app for your needs, even though they don’t always clearly label what they’re for. If you’re not trying to get pregnant, you still have to use other forms of contraception, even if the app doesn’t always spell it out for you. You have to trust the algorithms in the background and decide just how much information to provide — even if it’s not clear which symptoms you divulge might make the app work better for you.
Once you start filling in when you have chocolate cravings, you have to hope the app won’t turn around and use that information against you by alerting advertisers about your cocoa-vulnerability window. You have to hope that by dutifully logging your crippling cramp pains, that information will somehow help researchers find a better treatment one day.
Hopefully, if you rigorously record each time your period starts, the app will alert you that your cycle is getting longer and longer, which may be a sign of a health problem. You don’t want to be that blip in the data; that one or two in a hundred who gets pregnant, even though you’ve done everything the app requested.
“Ultimately, in some cases, for some people, I might recommend just use your calendar,” King said.
- Report finds most period tracking apps don’t protect privacy
- Are period tracking apps actually safe to use? Everything you need to know
- FDA clears first-ever smartphone app for insulin delivery
- Does tracking your sleep actually help you sleep better? We asked an expert
- Photograph your meal with the Foodvisor app for caloric, nutritional estimates