Q: What do you call people who use the rhythm method?
It’s one of the oldest birth control methods, and also one of the oldest jokes. The rhythm method, also known as natural family planning, involves tracking a woman’s ovulation cycle to determine when she can have unprotected sex without getting pregnant. As you can see from the joke above, it has a pretty bad reputation. And as you can see from statistics, that reputation isn’t unwarranted: The rhythm method is only 76 percent effective, according to Planned Parenthood.
That’s far worse than IUDs (more than 99 percent effective), birth control pills (91 percent for average use), condoms (85 percent for average use) and just barely better than the highly not-recommended pullout method (73 percent). It's no wonder that, on '90s TV sitcom Roseanne, a teenager who asked her mom if the rhythm method worked was told to “ask your brother.”
But recently, this much-maligned method has found itself in the spotlight—thanks to smartphone apps that help women track their fertility on their phone rather than on their own.
In February, the European Union approved one of these apps, called Natural Cycles, as a method of birth control for the first time. While no apps have yet been approved for medical use by the U.S. government, their popularity has been on the rise here, too: An Obstetrics & Gynecology study last year identified about 100 free, English-language apps that claim to help a woman track her period, get pregnant or avoid pregnancy.
(The inventor of Natural Cycles is looking into whether it could ever get approved in the states, where it’s also already available for download.)
Yet until now, there have been few peer-reviewed studies on how effective these birth control apps actually are at preventing pregnancy—and the limited research we have isn’t encouraging. One of the few, a 2016 study also published in Obstetrics & Gynecology, found that only four out of 53 period- and fertility-tracking apps and websites that the authors tested could accurately predict a hypothetical woman’s fertile window. Fortunately, that lack of data may be about to change.
This year, the Institute for Reproductive Health at Georgetown University began a study to test the effectiveness of one U.S.-based app, called Dot. Dot, which predicts when a woman might ovulate based on her period start date, has been downloaded 325,000 times since its debut in 2015 and currently has 53,000 active users, according to a representative for the company that developed it, Cycle Technologies.
The institute plans to follow 700 enrolled participants for 13 menstrual cycles, or about a year. Participants will provide their period start dates through the app, as well as daily information about when they have sex, whether they use a barrier method or emergency contraception, and whether they become pregnant.
Testing these apps “is really important because there are so many out there that are based on extremely questionable grounds and that make claims that are not backed up by evidence,” says Dr. Victoria Jennings, the institute’s director and principal investigator. (It's important to note that Cycle Technologies and the institute do have some history together, so the study isn’t fully independent; the company originally asked the Institute to conduct the study, says Cycle Technologies' president, Leslie Heyer.)
Today's glut of contraception options and the sometimes overwhelming influx of data on them can leave some women confused about their best bet for preventing an unwanted pregnancy. We asked: what, if anything, is really new about these birth control apps?
How it works
Birth control apps use a variety of markers to monitor your fertility, including the date of your last period, your level of cervical mucus and the presence of certain hormones. One of the common fertility markers they monitor is basal body temperature, or the temperature of the body during rest. Natural Cycles, the app approved in the EU, primarily uses the latter.
Using body temperature as a fertility indicator is nothing new. That’s because during “ovulation, your temperature goes up and stays up about half a degree,” says Dr. Mary Jane Minkin, a clinical professor of obstetrics, gynecology and reproductive sciences at the Yale School of Medicine. Natural Cycles basically gives this method a technical update, recording temperature by using a special thermometer sensitive enough to monitor changes and using it to alert women to their fertility level.
While Minkin hasn’t personally reviewed the technology behind the Natural Cycles app, as she understands it, “they’re using basically basal body temperatures to help predict ovulation, and just sort of automating it for an app,” she says. Using a woman’s body temperature, the app tells her whether her risk of pregnancy from unprotected sex is high or low. When the risk is high, women who don’t want to get pregnant are advised to abstain from sex or use a condom or diaphragm.
But there's a problem. “The crazy thing is that basal body temps are not that accurate as far as predicting ovulation,” Minkin continues. To be accurate, women need to take the test as soon as they wake up—if they go to the bathroom first, or get out of bed at all, they’ll mess it up. But even if a woman takes it right way, factors like illness, stress, alcohol consumption and irregular sleep patterns can still affect their temperature and their assessment of whether they’re ovulating.
In terms of technical advances, Minkin says the most accurate way to pinpoint ovulation isn’t to test your temperature: it’s to get an ovulation predictor kit. These are basically urine tests that check for Luteinizing Hormone, or LH, which is released prior to a woman's period. When you see a surge of LH, that means you will probably start ovulating within the next 12 to 36 hours. (Natural Cycles can also keep track of this hormone, which is released prior to your period, but this is optional).
Automating your calendar
By contrast, Dot is a bit more retro than Natural Cycles and other body temperature apps. In short, the app is an algorithm-based variation on the rhythm method technique known as the “calendar method.” This method goes way back: One of the earliest known references to it is a fourth-century text in which a Christian theologian chastises couples for avoiding sex on fertile days.
Yet instead of a woman calculating her “high-risk” days on her own, Dot promises to calculate them for her.
Because sperm can survive in a woman’s reproductive system for up to five days, the app’s high-risk days are supposed to start at least five days before a woman’s predicted ovulation. Yet some medical professionals like Minkin are skeptical of calendar-based methods like this. Minkin says the kits still encounter the same problem as all rhythm method-related tests: none of them can reliably predict ovulation at least five days in advance.
So if a woman finds out via one of the tests that she’s ovulating early, and she’s already had unprotected sex in the past few days, Minkin says “those little guys [i.e. sperm] might be around.”
According to Minkin, we just don’t have the medical technology to accurately predict ovulation five days in advance, every time. Given this, there’s only so much an algorithm can do. “The problem is that you don’t ovulate exactly the same time every month,” she says. “Many women will be off several days as far as ovulation, and if you’re basing it on past history, you’re not going to necessarily catch each ovulation.” Factors like stress and illness can also impact when a woman gets her period.
Jennings says that Dot is not intended for women whose cycles are outside the 20 to 40 day range. “A woman who has extremely variable cycles probably would quite honestly would want to look for a different method,” she says. Leslie Heyer, the founder and president of Cycle Technologies, defended the app’s ability to accurately predict ovulation in most women, but did note that it is not recommended for women whose cycles vary by 10 days or more.
Similarly, Elina Berglund—the Swedish scientist who created Natural Cycles app—says she thinks her app’s ideal user “is a woman in a stable relationship who is planning to have children at some point, and who would like a break from hormonal contraception ahead of trying,” according to a description in The Guardian.
So for women trying to avoid pregnancy, it's important to keep in mind that birth control apps are still evolving and being tested. For now, as Jennings puts it: “If somebody says, ‘It would ruin my life if I got pregnant right now,’” that woman needs to get something more consistent, like an IUD. “I think that’s common sense,” she says.