If you're trying to start a family, fertility apps like Glow, Clue and Ovia predict the times of the month women are most likely to conceive. Using them should help you get pregnant — if you know how to enter your information, and if your app is accurate. Illustration by Jim Cooke.
It's probably best to approach fertility apps as a tool to help you keep track of fertility signs. Even so, take the app's recommendation with a grain of salt. The idea behind tracking your cycle is legit, but getting the details right is tricky.
Why Fertility Tracking Isn't a Perfect Science
Fertility apps are essentially a special purpose calendar. You enter information each day, and the app calculates when you're most likely to conceive — your "fertile window". Timing is important because sperm can stay alive for a few days in your body, but your ovary only releases an egg on one day of the month. So the four or so days before ovulation are the days when sex can lead to pregnancy.
Unfortunately, there's no easy way to tell when you're about to ovulate. A calendar can help, since ovulation occurs about two weeks before your next period is due to start. But even this is tricky. Your cycles might vary in length, making ovulation hard to predict.
Fortunately, your body gives you other clues about when ovulation happens. You can learn to examine your cervical fluid, which becomes thicker and more slippery when you're most fertile. Another helpful clue is your body temperature, which bumps up by half a degree or so after ovulation. But your app can only track that change if you measure your temperature very consistently: First thing in the morning at the same time every day.
A Fertility App Is a Helpful Assistant, Not a Complete Solution
Full-featured fertility apps can track all three of these data points, plus other things that you might find helpful, like your mood and PMS symptoms.
You'll notice that most of the hard work occurs before any data goes into the app: You, in real life, have to notice what's going on with your body. And in the case of cervical fluid and body temperature, you need to know how to gather your data. There are books to help you (Taking Charge of Your Fertility by Toni Weschler is a classic) and even courses you can take.
That means these apps are just assistants. They're great at remembering data and colour-coding calendars, but if you can't tell the difference between fertile mucus and almost fertile mucus, it's not like the app is going to magically guess for you.
Even if you just want to keep track of your periods, these apps are still helpful. An app can send you reminders when your period is almost due, and provide a convenient way to answer the "When was your last period?" question that doctors always ask. And if you do have a surprise pregnancy, knowing the date of your last period makes it easy to calculate the fetus's age.
Fertility Apps Aren't Always Perfectly Accurate
There are a ton of fertility apps, and they don't all calculate the fertile window in the same way. One study, published earlier this year in Obstetrics & Gynecology, found that only three out of 33 apps could correctly calculate the fertile window for a standard 28-day cycle. (They were iPeriod, MyDays and Clue.) The researchers didn't test any other cycle lengths. "It's hard to predict how these apps would pan out in women with irregular cycles," lead author Robert Setton told me in an email. He also noted that we don't have any real world data on whether apps do or don't help people to get pregnant.
We do know that you're more likely to get pregnant if you have sex during the fertile window just before ovulation. But do apps really help you to pinpoint the dates of that window? Researchers at Georgetown University Medical Center are beginning a study on their fertility app, Dot, but results won't be available anytime soon. The makers of another app, Glow, conducted a study that they said showed women who use their app frequently got pregnant faster than women who only used it occasionally. The app helped people conceive faster, they concluded. But critics say the study couldn't rule out other plausible reasons for the difference, like the frequent users being more motivated to conceive and improving their chances in other ways.
Even though it makes sense that these apps should help you, we don't know for sure if they will. Also, the apps tell you when you are most fertile, but that's not the same as advising you when to have sex. Should you do it every day, every other day or every three days? Should you target your baby-making sessions for just your fertile window or forget the calendar and have sex all month long? Expert opinions sometimes differ, and an app won't help with that.
You Can Use Fertility Methods to Try to Prevent Pregnancy Too, but Beware
Since fertility awareness methods can tell you when you're likely to be fertile, you can use this information to avoid pregnancy if you like — essentially using the method as a form of birth control. If you never have unprotected sex on fertile days, it should be very hard to get pregnant.
This is actually a really effective method, if you get everything right. In theory, fertility awareness methods can be 97 per cent effective, on par with condoms or the pill. But in practice, it's easy to forget to log your data, or misremember the details about how to measure your temperature, or decide to throw caution to the wind on a day that turns out to have been a fertile day. Real life effectiveness can be much lower, 77 per cent for some methods.
Can apps help you to stay closer to the perfect-use numbers? A recent study published in the Journal of the American Board of Family Medicine found that most probably can't. The researchers scored apps based on whether they used an evidence-based method of fertility awareness, that is, a method that's been proven to work in previous studies. They also tested the apps against a few cycles of real women's data to see if they predicted the correct fertile window.
The apps with perfect or near-perfect accuracy were Sympto.org, LilyPro, LadyCycle, myNFP.net and the website Ovulation Mentor. Surprisingly, Glow was last on the list, with a score of zero. Part of the reason for Glow's failing grade, researchers said, was that their methods are kept secret. That means there is no way to tell if the app is using a method that's backed by science.
In the end, apps can help you to keep track of fertility-related information, although you should educate yourself so you know what data to collect and how to make sense of the results it gives you. If you prefer a lower-key approach, just track your period dates. Apps are great for that, too. It can be cool just to use an app to pay attention to what's going on in your body.
If you want to use fertility awareness methods to prevent pregnancy, make sure that you know what you're doing, and don't rely on an app to figure everything out for you. It's also worth considering how you would feel about a surprise pregnancy, since that's more of a possibility with this than with other, more reliable birth control methods.
Fertility apps are just tools to help you to keep track of your chances of conception, but we don't know how reliable they really are. They're not a silver bullet, nor are they a one-way ticket to a pregnancy if you're trying to have a baby. If you keep that in mind, you'll be able to use the apps as a fascinating — if imperfect — window into how your body works.