Apps that promise to help women “take control” of their sex lives by predicting the days they are fertile are putting users at risk of unwanted pregnancies by making misleading claims.
Millions of women in the UK – including 69% of young people aged 18 to 24 – have used smartphone apps that track their periods. Many also tell them their “fertile window”: the days in which they are most and least likely to get pregnant.
But the quality of the data used to make these predictions varies dramatically and is often limited and unreliable, experts warn. Most apps use only the user’s previous period dates and standard cycle information to predict when their next period will be and, by extension, when they are likely to ovulate and be most fertile.
Despite this, apps that use only basic data are being widely promoted to women in the UK as a reliable form of contraception. A Observer An analysis of fertility and period tracking apps in the Apple and Android stores last week found that some that are not registered as medical devices are described as “contraceptives” and claim to be “as effective as condoms.”
One, called Period & Fertility Tracker, bills itself as an “ovulation tracker” and says it’s based on “scientific research” that “helps determine the fertile days of the month, so you can achieve or avoid pregnancy.” . However, its predictions are based solely on information entered by the user about the dates and length of their period.
Another, called Cycles, says it is a “fertility and ovulation app” and promises “accurate” daily predictions about a high or low chance of getting pregnant. Their website includes a disclaimer stating that it is “for information only.” But the app’s description promises “no more surprises, worries or feelings of darkness” and invites people to make the app their “trusted partner in healthcare.” It is based on the standard days methodwhich is among the least effective contraceptive options.
Other apps offer the ability to “manage your fertility goals,” “postpone pregnancy,” and “check your chances of conceiving each day.” One of them tells women that it can “predict their chances of pregnancy” so they can “take control of their sex life” and “feel good in bed.” Some have been downloaded millions of times. Almost all are unregulated and many are based outside the UK.
The apps are being promoted amid concerns about a rise in the proportion of women using “natural contraceptives” and abandoning hormonal contraceptives. Last week, a study using data from the British Pregnancy Advisory Service (BPAS), published in the B.M.J.said 2.5% of women seeking an abortion in England and Wales in 2023 reported they had been using natural methods, such as fertility monitoring, at the time they became pregnant, up from 0.4% in 2018.
Those who reported not using contraception when they became pregnant increased to 70% in 2023, up from 56% in 2018. While the study did not show a direct causal link, the researchers said a small but significant increase was needed in people who They used “natural” methods. investigated further and raised concerns about the accuracy of apps that predict fertility windows.
The apps are mainly based on traditional fertility awareness methods which are mainly based on date tracking. They have been used for centuries to estimate chances of conception, but can be risky due to the possibility of human error and individual body fluctuations. He NHS says About 24 out of every 100 women a year will get pregnant using “natural family planning” if they don’t do it completely correctly.
Some apps also require users to enter daily data about their body temperature or cervical mucus, which can increase accuracy. Between two and 23 out of every 100 people who use natural contraceptives become pregnant each year, depending on the method they use, the researchers said.
Previous research on apps that offer fertility predictions has found that they are generally of poor quality, with a 2017 review Of 73 calendar method tracking apps found that none could accurately predict ovulation, and otherIn 2016, it found that only six out of 40 apps had perfect accuracy in predicting the user’s fertile window.
Still, women are often given black-and-white predictions, telling them whether they are “fertile” or “non-fertile” on a given day, which they could use to make decisions about unprotected sex.
Dr Janet Barter, president of the Faculty of Sexual and Reproductive Health (FSRH), said: “Knowing when your periods are doesn’t necessarily tell you when you’re ovulating, so you need more than that to be effective.” .”
The findings have sparked calls for the regulator to take drastic action to address the “clear dangers” posed by unregulated apps. The Medicines and Healthcare products Regulatory Agency (MHRSA), which oversees contraceptive devices, says that “health apps designed to be used as contraceptives or to support conception are likely to be considered medical devices.” This includes those that “claim to be directly capable of increasing the likelihood of pregnancy or preventing pregnancy”, which should “carry a UKCA or CE mark to demonstrate that they meet the requirements of the legislation and are acceptably safe”. A spokesperson said all alleged breaches were investigated.
But many apps appear to be avoiding oversight because regulation depends on manufacturers self-reporting the “intended purpose” of their product. This means that period trackers with fertile window features generally fall into the same category as health and fitness apps, which are generally not classified as medical devices, rather than contraceptive devices, which are.
Currently, only one app, which uses basal body temperature monitoring to make predictions, has been granted permission to market as a form of birth control. Natural Cycles, which advertises widely in influencer-sponsored posts on TikTok and Instagram, claims to have a 93% effectiveness rate for typical use.
But many experts consider even Natural Cycles to be risky because it relies heavily on the user to enter their data regularly and accurately and to abstain from sex or use alternative protection on fertile days. While it has been approved for use as a contraceptive in the US, in the UK, a review by Nice in 2021 found there was insufficient evidence for it to be approved for use on the NHS.
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In July, the Society of Obstetricians and Gynecologists of Canada (SOGC) raised concerns that the app’s effectiveness may be overstated and warned users to “avoid unprotected sex, especially while monitoring initial cycles.”
Natural Cycles rejected the criticism, saying its evidence was strong; that more research had been carried out since the Nice review was published; and that the SOGC lacked understanding of its product.
A spokesperson said that typical use of the app was “comparable to other contraceptive methods, both hormonal and non-hormonal”, adding that “although a head-to-head trial comparing these methods in the contraceptive sector has not yet been conducted Natural Cycles is classified in the same category of effectiveness as methods like the pill.”
Dr Catriona McMillan, professor of law and medical ethics at the University of Edinburgh, said the app market was currently a “wild west”. “Many of them can be downloaded for free and many indicate a woman’s fertile window. The worrying reason is that period tracking apps are not a medical device at all. “They are not regulated at all, except by advertising and data regulators,” he said.
There is growing evidence, he added, that younger people are “stopping using things like the pill, the IUD and the coil device,” in part because of concerns about side effects. problems accessing medical care and disinformation on social media and turn to period tracking apps instead.
“But since they are not a medical device, the data they use to make these calculations can be from one person, two or ten people. They don’t need to have an evidence base. Therefore, fertility windows are often calculated incorrectly. And when young women depend on these, they can get pregnant very easily because the algorithms do not always work.”
McMillan called for all apps that offer fertility predictions to be registered as medical devices. She believes that apps should, at a minimum, be required to include disclaimers stating that they should not be used for contraception. But he said that, in reality, this might not be enough: “How often do you read the description of an app or visit the website?”
Dr. Chelsea Polis, a reproductive health scientist and digital contraception expert, said: “Given what we know about how inaccurate many estimates of fertile windows are, apps that are untested and insufficiently regulated may actually put people at risk of unwanted pregnancies. But many period tracking technologies are excluded from a higher level of scrutiny because manufacturers do not label them as medical devices.”
FSRH’s Barter said the rise of “natural contraceptives” and the fact that people report not using any contraception raise bigger questions for women’s health.
In a 2024 survey by BPAS, almost half of women reported facing barriers to accessing contraception, including long wait times and difficulties getting appointments, as well as cost. A significant majority (84%) said they had changed their contraceptive methods at least once, and one in seven were unhappy with the side effects of their current method.
“I think we should all be more concerned about finding birth control that women feel comfortable with, rather than trying to persuade them to feel more comfortable with what we have,” Barter said.