In many ways, family planning based on keeping track of one's fertility is about as old-school as it gets. By paying attention to fluctuations in body temperature or cervical fluid, women can track when they're ovulating and time intercourse so as to increase or decrease their odds of getting pregnant.
Currently, a slew of fertility tracking apps are working to bring family planning into the smartphone era. And now a new app aimed specifically at preventing pregnancy, called Natural Cycles, has hit the market, claiming to identify a woman's non-fertile days when she is 99 percent safe to have unprotected sex without conceiving.
Created by two physicists in Sweden, the app uses -- as the company's website describes it -- "statistics and analytics instead of chemicals or surgical procedures in order to prevent pregnancies," by helping women pinpoint the handful of days per menstrual cycle when they have the greatest chance of getting pregnant.
In practice, that means users pay roughly $70 per year for a high-tech version of the temperature method of fertility awareness. First thing in the morning, before she moves too much or gets out of bed, a woman using Natural Cycles will take her basal body temperature and record it in her phone. She can also use ovulation-predictor strips or kits, which measure increases in luteinizing hormone -- a potential predictor that ovulation is soon on the way.
The app works by warning the user about her fertile window -- the stretch of days before ovulation when she is most fertile. Women's resting body temperatures generally rise when they ovulate, and the app uses that information to tell the user when she is ovulating, when she has ovulated and when she is likely to ovulate. It divides her cycles into "red" days, when she's more likely to get pregnant having unprotected sex and "green" days, when she's outside her fertile window. According to Natural Cycles, the "green" days are 99 percent safe to have unprotected sex without conceiving. If the app is unsure of a user's fertility status because she hasn't provided enough data, she will simply get more red days.
Raoul Scherwitzl, CEO and co-founder of Natural Cycles, told The Huffington Post that what sets his app apart is its "complex" algorithm, the details of which are slated for publication in a forthcoming study of more than 300 women that retrospectively gauges the app's ability to identify ovulation. The app analyzes women's biomarkers for them, said Scherwitzl, so all they have to do is insert their daily temperatures and results from the optional ovulation predictor strips.
"The problem that usually comes with [fertility charting] is that when women look at the charts, the data is usually fluctuating with data points going up and down," he told HuffPost. "It can be very hard [for a woman] to look by eye and make objective decisions on whether she's fertile that day or not."
"We developed an algorithm that analyzes the data," he continued, "so a woman doesn't need to learn about 'What does it mean if [temperatures] go up and down?' She just needs to measure, then we tell her when she is safe or at risk."
But outside experts warn that at least until the forthcoming study is published, it is too soon to weigh many of the claims about the app's efficacy. And of course, the app does nothing to protect the user from sexually transmitted infection.
"Basal-body temperature, which is what their app is based on, and what their methodology appears to be based on, is a very accurate marker," said Dr. Victoria Jennings, director and principal investigator of the Institute for Reproductive Health at Georgetown University, which she said is very interested in fertility awareness methods.
The problem, said Jennings, is that the progesterone spike that increases a woman's resting temperature does not necessarily occur early enough in her menstrual cycle in order for her to effectively avoid pregnancy, because sperm can survive in a woman's body for up to five days, limiting its predictive value. That is why researchers have not established clear-cut efficacy rates for methods like temperature tracking. (Generally speaking, Planned Parenthood estimates that 24 out of every 100 couples who use fertility awareness-based methods in a year will get pregnant if they don't always use the method correctly or consistently. The organization notes that always practicing the methods correctly does make them more effective.)
Still, that doesn't mean Jennings sees no value in apps that aim to help women predict when they should or shouldn't have sex in order to achieve or prevent pregnancy. On the contrary.
"There are some claims that the inventors of this app make that I do agree with, and one is that many women would like to have a natural option, one that does not involve putting something into their bodies, and they're willing to do something to make that happen," said Jennings. "I think that really needs to be acknowledged, and the degree to which we can create things that will help women in that way, we need to do that."
Correction: A previous version of this article stated users of the pregnancy prevention program also see "yellow" days on the app.