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It sounds like a dream: opening an app instead of taking a birth control pill. Swiping and clicking instead of fumbling with a condom. But before you get too, uh, excited, it's not as miraculous as it sounds.

This birth control app is called Natural Cycles. It's billing itself as “the only approved contraceptive app out there,” and after you input a lot of information and it gets to know your body's patterns over the course of several months, this handy app can determine your fertile periods and tell you when to avoid sex. (It can also be used in the reverse by couples trying to get pregnant.)

The app, which is now available for iOS and Android, was designed by a husband and wife team of two physicists, Dr. Elina Berglund and Dr. Raoul Scherwitzl. They initially developed the algorithm for their own use and then decided to turn it into an app for everyone. They have gone to a lot of trouble to have it an approved and CE marked as medical device.

What does this mean for you? Essentially it means they've had to meet quality assurance and development standards set by German testing organization Tüv Süd, and they are now the only fertility app that has earned their approval.

While it's been proven to be very good at what it is, it's essentially the rhythm method 2.0: a souped up version of what women have been doing for decades, charting their temps. The app's tracking system is based on the Fertility Awareness Method, a widely used way of monitoring ovulation using your basal body temperature.

You use a basal body thermometer (which offers a more precise measurement than the kind you’d use to see if you have a fever) to take your temperature first thing in the morning. You input that information into the app, and it’s algorithm uses it to tell you whether it’s a “green” day, when it’s fine to have unprotected sex, or a “red” day when you are fertile and should use protection or abstain.

Sounds simple enough. And they’re pitching this product as a side-effect free alternative to hormonal birth control and an improvement on using inconvenient and clumsy barrier methods during the entire month. But the truth is that Natural Cycles is hardly the one-size miracle solution we’ve all been waiting for.

For one thing, the fertility awareness method is best for people who are in a committed relationship with a single partner, have a regular enough schedule to allow for accurate temperature charting, and the discipline to be consistent and to abstain from sex (or use protection) when necessary.

You also have to be in a position to be okay with getting pregnant if the method fails. After all it is an app, and even a fully regulated and certified one can make mistakes.

That rules out a lot of people! Of course other methods of birth control require some degree of consistency (gotta take that pill every day) and discipline (gotta use that condom) too. But there is a lot of potential user error with this method -- and it offers no STD protection, if that's a concern.

That said, according to a study the makers of this app conducted, if you do a reasonable job of inputting data on a regular basis, using Natural Cycles is as effective at preventing pregnancy as the pill. It's more effective than using condoms alone, but it's less effective than an IUD. Obviously, no birth control method is 100% effective all the time for everyone.

If you do decide you are ready to hop aboard the natural family planning train, this isa pretty sophisticated way of doing it. Their algorithm factors in things like sperm survival times and cycle irregularities.

Still, LH testing is really the only surefire way to know in an at-home setting that you are, in fact, about to ovulate. (That typically means dipping a special stick into your urine to measure luteinizing hormone, which is produced by your pituitary gland and surges quickly right before ovulation occurs.) Natural Cycles does give you the option of inputting LH test results to improve its accuracy even further.

But here's the thing: this app requires a paid subscription. At the moment, the cheapest plan costs $6 a month for the year and includes a thermometer. A monthly plan will run you $10 with no thermometer included. (There's also a one month free trial.) Neither plan includes a way to test your LH levels.

So you're paying for the app, you're measuring your temperature first thing every morning (and hand-inputting it into your phone) and if you really want to be diligent, you're also monitoring your LH levels. And, if you do everything right, you're probably getting a very pinpointed idea of when you should not have sex. Great.

But you could also just measure your temperature on your own, keeping track of it in one of the many free fertility apps already available. (Or even on old-fashioned paper like our foremothers did. Gasp!) Or you could just use a fertility monitor that measures LH levels, which aren't cheap but it's just a one-step process instead of three or four. Or you always could try one of the many new wearables or IoT devices designed to help you track your cycles.

The point is that while this particular app is far better regulated and held to a much higher quality assurance level than a lot of the other options in the very crowded app market, it's still just an app. If you’re a person for whom the fertility awareness method is a good fit, then this can certainly be an effective (if unnecessarily complicated and expensive) way of practicing it.

But if your primary concern is remaining fetus-free without a ton of hassle, then put your phone down and get yourself an IUD.

Correction: An earlier version of this story incorrectly stated that the app can be prescribed by doctors in Europe and the UK.

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