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If you’ve texted, DMed, or spoken aloud the words “birth control” to your friends sometime in the last few years, you’ve probably seen ads proclaiming that there’s an app for that. Several companies promise that tracking your menstrual cycle with their app and their algorithm will help you prevent pregnancy—no hormones, implants, or IUD insertions required.
All birth control apps rely on a contraceptive technique that’s been around forever called fertility awareness: Basically, you log certain physical traits every single day to track your menstrual cycle until you can predict ovulation like clockwork. Avoid unprotected sex on the days during and around ovulation, and you’re unlikely to get pregnant. When done correctly, this method is effective—but precisely how effective is a matter of some debate.
This is what has led to controversies around birth control apps like Daysy and Natural Cycles. As with any birth control method, the efficacy of fertility awareness depends on how correctly and consistently you’re using it. But unlike condoms or the pill, we don’t have a clear picture of what “average” fertility awareness use looks like—and there’s little scientific consensus about the quality of the studies behind those “93% effective!” claims. FDA-approved app Natural Cycles has had their efficacy claims investigated and cleared by Swedish medical authorities, but the UK found them misleading enough to ban some of its advertisements. Despite serious allegations of improper data collection and analysis, Daysy is still on the market today. All of this makes it tricky for potential users to see past the hype and make an informed contraceptive decision.
On top of that, there is a lot of misinformation out there about fertility awareness contraception in general. Hardcore proponents often overstate its effectiveness, while skeptics are too quick to dismiss it outright—making some pretty gross assumptions along the way about the people who use them. To set the record straight, I talked to research scientist Dr. Chelsea Polis and OB/GYN Dr. Rachel Peragallo Urrutia, who have conducted a systematic review of fertility awareness studies. If you’re intrigued by the idea of a birth control app, or if you just want to know more about fertility awareness, here’s (almost) everything you need to know to decide if it’s right for you.
What is fertility awareness-based contraception?
Fertility awareness-based methods, or FABMs, aim to prevent pregnancy by dividing the menstrual cycle into “fertile” and “non-fertile” days. On fertile days, the likelihood of getting pregnant from unprotected sex is at its highest; on non-fertile days, it’s at its lowest. Figuring out which days are which is accomplished by carefully tracking biomarkers, or physical indicators of how far along you are in your cycle.
There are a few relevant biomarkers you can track, which means there are multiple FABMs to choose from. These are the most common types:
Calendar methods, like the traditional “rhythm method,” track fertility by the calendar days of a menstrual cycle. Once you’re familiar with the length and regularity of your periods, you can use the standard menstrual cycle timeline to identify your most and least fertile days. In the Standard Days method, for example, cycle days 8-19 are considered fertile.
Cervical mucus (or ovulation) methods track ovulation by observing changes in cervical mucus, which is exactly what it sounds like: mucus that comes out of your cervix. Its consistency and appearance change in response to the hormonal fluctuations of the menstrual cycle, becoming characteristically stretchy and slippery right before ovulation. The simplest mucus method is the Two-Day method: Any day you observe this mucus counts as fertile, as does the day before.
Basal body temperature (BBT) methods also track ovulation, which causes a slight but measurable increase in body temperature. Every morning, before you get out of bed, you take your temperature and record the reading on an app or manually on graph paper. However you record the readings, the goal is the same: to identify the temperature spikes that accompany ovulation. The Natural Cycles app, which can use temperature data from the Oura ring or the Samsung Galaxy watch, is an example of a BBT method.
Urinary hormone-based methods use a device called a contraception monitor to test the levels of estrogen and other hormones in your urine. These measurements are fed into an algorithm that calculates the fertile window.
Any of these single-biomarker methods can prevent pregnancy when used properly, but you can also combine them for extra information. Using the BBT method in conjunction with calendar and/or mucus methods is a symptothermal method; swapping BBT for urinary hormone makes it a symptohormonal method.
This sounds a lot like Natural Family Planning (NFP)—are they the same thing?
Yes and no. Scientifically, there’s no real difference—NFP and FABMs use the same techniques—but there often is a meaningful difference in their social and moral framings. As the Association of Fertility Awareness Professionals (AFAP) explains, NFP is traditionally taught in a Catholic context:
“Most NFP methods advocate chaste abstinence (refraining from all sexual activity) during the fertile phase of the cycle if a couple wishes to avoid pregnancy. NFP does not condone sexual activity outside of marriage and often restricts instruction to heterosexual, engaged or married couples.”
By contrast, fertility awareness is deliberately inclusive. The AFAP welcomes all people regardless of gender, sexual orientation, religion, or marital status, and they explicitly support “the full range of reproductive options”—including condoms, fertility treatments, and abortion.
Advantages of fertility awareness methods
The most important thing to remember about FABMs is that they’re nothing more and nothing less than another birth control option. Just like any other method, you have to weigh the pros and cons.
No hormones mean no hormonal side effects
Hormonal birth control comes with side effects; there’s no way around it. While some of them can be positive—lighter periods, less acne, milder PMS—finding the right cocktail of hormones can take literal years of trial and error. For this and other reasons, non-hormonal methods like FABMs have their advantages: like copper IUDs and condoms, a FABM won’t induce unpleasant hormonal side effects. But unlike IUDs, FABMs require no painful insertion process and won’t alter your periods—and, unlike most condoms, a latex allergy isn’t a dealbreaker.
Many methods are free or low-cost
Physical and financial accessibility is another plus for FABMs. Once you know what you’re doing, the only equipment you need to check your cervical mucus is your cervix, a finger, and a calendar or chart. You take the measurements by yourself, on your own schedule, in the privacy of your own home.
Of course, some companies are eager to monetize fertility awareness, particularly on the instruction side. In itself, this isn’t necessarily a bad thing: proper use requires a level of expertise. Classes or individual consultations with licensed practitioners aren’t free, but many are low-cost or charged on a sliding scale. And while neither are strictly necessary, a fancy thermometer and an app subscription could still end up costing less than an ob/gyn appointment and a monthly prescription, depending on your insurance.
All the power is in your (and your partner’s) hands
Tracking and recording biomarkers every day for years gives you a fuller picture of your reproductive health than taking a pill or occasionally remembering that your IUD exists. Depending on how much you enjoy tracking health metrics—and your experiences within the healthcare system—this can be downright empowering.
Using a FABM also requires strong communication with your partner(s) and medical practitioners. For people in healthy, mutually supportive relationships, the teamwork can be rewarding; from a clinician’s perspective, treating a patient with an informed, invested interest in their health is a pleasure. Urrutia told me she loves fertility awareness counseling because it represents “a true partnership” between her and the patient.
What are the disadvantages of fertility awareness contraception?
Depending on your perspective, the biggest advantage of FABMs may also be their biggest drawback. These methods are the opposite of “set it and forget it”—they require daily active participation from at least two people, making them especially susceptible to human error. But besides that, one of the most frustrating hurdles in learning about FABMs is how little we know for sure about their usage and efficacy.
It’s not immediately effective
Switching to a FABM is neither fast nor easy. There’s a ramp-up period involved, during which you track your biomarker(s) of choice every day, ideally without having unprotected sex at all. Even if your periods are like clockwork, this introductory period can last for one to three cycles: You need to know what “normal” looks like, but you also need time to get used to the techniques.
Irregular periods complicate the onboarding process. If you’re coming off the pill, are recently postpartum and/or breastfeeding, perimenopausal, or have a medical condition that causes irregular periods, it could take longer—up to six months—to establish that baseline. The bottom line, according to Urrutia? “You can’t just jump right in.” In other words, until you’ve really gotten the hang of biomarker tracking and done it long enough to accurately predict fertile days, you can’t rely on a FABM alone to prevent pregnancy.
There’s no STI or STD protection
As with any non-barrier contraceptive, FABMs do not protect you from sexually transmitted infections or diseases. If your sex life involves any risk of infection and you rely on a FABM to prevent pregnancy, be sure to use a barrier method, like condoms, to prevent STIs.
Do fertility awareness methods actually work?
Nearly every other contraceptive method has been studied to death. We know to a very high degree of certainty how many people use the pill, how reliably they use it, and how often the pill fails with typical or perfect use.
Pretty much none of this holds true for FABMs, which are rarely the focus of clinical trials. Since they’re not widely used, this makes some sense; the potential pool of study participants starts small and keeps shrinking as exclusionary criteria are applied. The data behind fertility apps often come from privately funded labs, so they’re proprietary—you can’t just Google the results. Even peer-reviewed papers on FABMs aren’t always reliable: They may be statistically underpowered, rely on self-reported or cherry-picked data, exhibit seriously flawed experimental design, or all three. Some studies even lump all FABMs into one method, which glosses over the wide variance in their efficacy rates.
Unfortunately, all of this means that there’s a serious lack of peer-reviewed data for FABMs—and when it comes to informed decision-making, this is the biggest hurdle for providers and patients alike.
Perfect- and typical-use effectiveness isn’t well-defined
Of the roughly zillions of criteria to consider when choosing a contraceptive, most people focus on two numbers: its effectiveness with perfect use, and its effectiveness with typical use. Knowing what differentiates the two—and your tolerance for that difference—is crucially important.
Perfect use is more or less what it sounds like: using the contraceptive method exactly as instructed every single time. Polis defines it as “[The] effectiveness that we would expect for somebody who, every single time, uses the method correctly and consistently.” Obviously, this is when contraception is most effective; perfect use results in high effectiveness or low failure rates, depending on your perspective.
Typical use, she explains, is less straightforward. “In a nutshell, typical use is the effectiveness that you might expect for an average person. … It includes some leeway for not perfectly following the instructions for the method every single time you use it.” This means that typical use effectiveness rates are lower (and failure rates are higher) than what you’d get with perfect use.
The definitions of typical and perfect use don’t change from method to method, but what they actually look like does. As Dr. Polis explained, perfect FABM use needs to check a whole lot of boxes: “[It requires] perfectly tracking all of the biomarkers involved in the use of that method, perfectly interpreting them, and then perfectly avoiding unprotected sex on every single day that’s calculated as being fertile.”
If you can consistently check those boxes, FABMs are effective, but reliable data on perfect use can be hard to come by. According to the systematic review that Urrutia and Polis published, one study showed that the mucus-only Billings Ovulation method can result in as few as one unplanned pregnancy per 100 person-years when used absolutely perfectly. In other words, if 100 people used the Billings Ovulation method perfectly for a year, we’d expect to see one unplanned pregnancy. For the Standard Days calendar method, that number is 5; for the Two-Day mucus-only method, it’s 3.5.
Typical use data for FABMs is a bit easier to find—for some methods, that’s all we have—but the numbers are inconsistent, even within methods. With typical use, the Billings method could result in as few as 10 or as many as 33 unplanned pregnancies per 100 person-years, depending on the study. For Standard Days, it’s 11-14 pregnancies; 14 for Two-Day. Even if you know that typical use reduces effectiveness and are realistic about your behaviors, there’s a big difference between 10 and 33 unplanned pregnancies.
This is largely why the discourse around FABMs is so ripe with misinformation. Without reproducible, rigorously-tested efficacy data from independent studies, it’s hard to know exactly what you’re signing up for—especially once marketing jargon gets involved. Natural Cycles and DaysyView, which both use the BBT method, have faced backlash over their advertised typical use effectiveness rates. But investigating the merit of those accusations, and then taking action if they’re legit, can be a painfully arduous process. In June 2018, Polis published a critique of the study used in DaysyView’s marketing in Reproductive Health (which also published the original study), citing serious analytical and methodological flaws. Based on her commentary, the article was retracted—but the company that made Daysy sued her. (The suit was eventually dismissed.)
How to choose a method that works for you
If the pros and cons of FABMs line up with your lifestyle, and you’d like to get started, you’ll have to do some research first. But conducting medical research on the Internet is complicated, confusing, and potentially dangerous. How can you filter out the chaff?
Seek out high-quality sources
According to Polis, the best thing you can do is avoid hype. There are lots of people who’d like to profit from your decision to use an FABM, whether with a slick-looking app, an expensive training program, or even a book. In that vein, she has a specific recommendation: “Try to avoid looking to social media influencers to help you make your contraceptive decisions.” With that said, it’s possible to get quality information from for-profit sources as long as you know what to look for, which is a detailed, clear explanation of all the risks and benefits.
If you’re just starting out and don’t know where to turn, try FABM FAQs from Planned Parenthood, the AFAP and the American College of Obstetricians and Gynecologists (ACOG). For more in-depth discussion that’s still user-friendly, Polis has a Twitter feed where she talks about all things contraception; Reply OB/GYN, where Urrutia practices, has an entire page dedicated to FABMs. If you’d rather go straight for the literature, the Guttmacher Institute is a wonderful resource.
If you can, find a qualified professional
Certain FABMs (notably Billings Ovulation, Marquette, and Sensiplan) actually require instruction by a professional who’s certified to teach that particular method. There’s no federal accreditation board; certificates vary by method. If you’re interested in any FABM, particularly one that requires instruction, use the AFAP practitioner directory to locate a qualified educator in your area, or online—most practitioners offer virtual consultations.
It’s worth noting that while a trusted doctor can be a fantastic guide, your ob/gyn may not be able to help; as Urrutia explained to me, FABMs aren’t a part of formal ob/gyn education. The upside of this is that doctors who do offer FABM counseling (like Urrutia) usually do so out of a genuine passion for the work—so if you can find one, they’ll probably be psyched to work with you.
Be honest with yourself and your doctor
When counseling a patient interested in FABMs, Urrutia’s main goal is to understand their reproductive plans. This involves a lot of questions, all of which need to be answered honestly and completely in order for her to make a recommendation: “Do you want to have kids? Do you want to have more kids? When do you want to have [those] kids? What’s your relationship like? … How much work do you want to do in making sure that your method’s effective? What [birth control methods] have you used in the past, and how has that been for you?” She also specifically mentioned that screening patients for intimate partner violence is a crucial part of this assessment: FABMs require the kind of mutual trust, respect, and honesty that doesn’t exist in a physically or emotionally abusive relationship.
If this seems like a lot to take in, it is. Choosing a contraceptive method is a massive, potentially life-altering decision—and you deserve to know what you’re getting into. Know yourself, know your dealbreakers, and take all the time you need to make the best decision you can.
Updated April 2019: Edited to clarify that Natural Cycles advertisements were banned by the UK’s Advertising Standards Authority, not the app itself. Additionally, the study used in Daysy’s marketing materials is a retrospective survey, not a clinical trial.
Updated Sept. 1, 2023: Edited to note that after our initial publication, the Daysy study was retracted, the company sued Polis, and the suit was later dropped.
