Can an app really tell you when you’re fertile?

Your grandmother might have tracked it on her calendar, but keeping track of your menstrual cycle today is as easy as a few taps in an app. Fertility awareness methods involve various strategies for identifying a woman’s fertile window to time sex for either preventing or planning pregnancy. In 2009, only about five percent of Canadian women aged 30 to 39 relied on these methods as a form of contraception. But since then, smartphones have changed how we do just about everything.

A 2016 study in the Journal of the American Board of Family Medicine found nearly 100 smartphone apps that allow women to track their fertility and menstrual cycles. Considering that the most popular of those have been downloaded over a million times each, it’s clear that women are turning to technology to keep track of their cycles and their fertility.

Recently, the fertility awareness method that has been getting a lot of attention in the app world is the sympto-thermal method (STM). The method tracks three bodily clues—your period, temperature and cervical fluid—to predict your fertile window. Your period usually occurs 14 days after ovulation, while your temperature rises by about 0.5 to 1.5C within 12 to 24 hours after ovulation. By taking your temperature daily when you first wake up—known as your basal body temperature (BBT)—you can better pinpoint when you’ll ovulate. Finally, the consistency of your cervical mucus changes during ovulation.

“When your body is ovulating, that fluid becomes like egg white—thin and stringy—which is really different from the denser, tackier fluid produced when your body isn’t fertile,” says Kristen Gilbert, education director at Options for Sexual Health in Vancouver. Tracking these events over several months can reveal a pattern that can help you—and your app—predict when you will ovulate the following month.

The daily commitment involved in STM doesn’t exactly scream convenience, which is why apps like Kindara, Lily and Fertility Friend are so revolutionary. Instead of charting every element by hand and counting forward to predict when it will occur next month, users simply tap a few buttons to input their information and an algorithm does the rest, predicting when they’re fertile.

Some apps even come with the option of purchasing a specially designed Bluetooth-enabled thermometer that directly inputs your temperature each day. It’s still a process—you have to wait several cycles for the algorithm to accurately predict your fertile window—but it becomes more accurate with time. The more cycles you input, the more accurate the prediction.

Some apps allow you to set a goal to prevent pregnancy or get pregnant. Users looking to avoid pregnancy may receive a message like “Use protection” on their fertile days or a blinking red circle on their digital calendars. On the other hand, if you’re trying for a baby, one app will tell you how fertile you are through a series of coloured stars that darken in hue based on how fertile you are that day. These apps seem like they take fertility awareness to a whole new level of effectiveness, but do they?

As a conception tool, fertility tracking apps can be a good guide to understanding your fertility and maximizing your ovulation window. “I talk to my patients about tracking apps to predict ovulation,” says Yolanda Kirkham, an OB-GYN who works at Women’s College Hospital and St. Joseph’s Health Centre in Toronto, “but some are better than others.”

A 2016 study in the Journal of the American Board of Family Medicine tested 30 fertility awareness apps. Of the 12 apps that used STM, only four—Lily Pro, Lady Cycle, Sympto.org and mfNFP.net—received perfect scores for accurately predicting their users’ fertile days.

Fertility apps also fall short when compared to at-home ovulation predictor kits. Though the apps simply use past signs of ovulation to predict what will likely happen in the coming month, ovulation predictor kits use current bodily clues to advise users when they are about to ovulate. According to a 2015 study in the Journal of Women’s Health Care, an ovulation predictor kit that looks for hormonal changes in saliva is 93 percent accurate, while a 2011 study in the Canadian Medical Association Journal that looked at two urine-testing ovulation predictor kits found they were up to 97 percent accurate.

For couples using fertility awareness methods as birth control—whether on an app or tracking by hand—about 24 percent get pregnant each year, says Kirkham. “That’s similar to withdrawal, where 22 percent get pregnant each year.” Meanwhile, the pill lets only one percent of users conceive, and an IUD boasts a failure rate of between 0.2 and 0.8 percent. “Using the app might be easier than plotting on a piece of paper, but it doesn’t raise efficacy to the levels of hormonal contraception and IUDs,” says Gilbert.

Part of the problem is that, despite the fact that apps use high-tech algorithms, human error still comes into play—and, of course, the app has to have been programmed correctly. There’s also the fact that these apps won’t work as well for women with irregular cycles. “We aren’t robots, and our bodies are unpredictable,” says Kirkham. Predicting a pattern to determine your fertile window can prove challenging if your cycle varies from month to month, even when done digitally.

Most apps boast comforting statistics regarding their efficacy, but these numbers should be examined closely. “There are some dramatic claims that I don’t think we can rely on,” says Gilbert.

Kindara, for example, says it’s based on a method that is 99.6 percent effective, yet the fine print states that it advises women to have “their charts reviewed by an expert” before relying on the app as a sole method of preventing pregnancy.

Gilbert advises potential users to do their homework and choose an app that is easy to use and doesn’t make extraordinary claims. Or, as Kirkham puts it, “User beware.”

Read more:
5 signs you’re ovulating Everything you need to know about birth control