How do period-tracking apps work, and should you use them for fertility?

The number of women in England and Wales turning their backs on the contraceptive pill and using period-tracking apps has risen steadily, as many women look for more "natural" ways of managing their fertility.

Fertility or period tracker apps have been growing in popularity since 2021, with apps like Clue, Flo and Period Tracker dominating the market. But although only a small number of apps market themselves as a contraceptive tool, two of the most common reasons for using them is to either achieve or prevent pregnancy.

A new study suggests the risk of unplanned pregnancies has risen alongside the popularity of period tracker apps. The researchers found that women’s attitudes have shifted from "more reliable" hormonal contraception in the last five years, in favour of "fertility awareness-based methods".

However, this move corresponds with a rise in abortion rates, the researchers said, pointing to a potential increase in "unintended pregnancies" among women who rely on these apps.

Writing in the journal BMJ Sexual & Reproductive Health, experts at the University of Edinburgh said: "While the rise in abortion rates is multifactorial, one aspect that needs scrutiny is any change in contraceptive use, and particularly this surge in the use of e-health, including fertility apps, period-tracker apps, and natural family-planning apps."

Here’s everything you need to know about period-tracker apps, from how they work to whether you should use them to keep track of your fertility.

How do period-tracker apps work?

Period-tracker apps are aimed at helping women understand their menstrual cycle and predict when they will be in certain stages of menstruation, such as ovulation.

Users will be asked to enter personal data, including period dates and symptoms, mood, energy levels, and even sexual activity. The apps then use algorithms to predict things like when your period will arrive and how long it will last.

They also use these algorithms to predict your ovulation dates and your "fertile window". This is the time during a menstrual cycle when you are most likely to get pregnant, and some users use this prediction for fertility planning.

Some apps ask for more intimate and sensitive information, such as daily body temperature. The BBC reported last year that some even ask for information about abortions and miscarriages.

What are the risks involved with period-tracking apps?

While period-tracking apps promise women a better understanding of their menstrual cycles, there have been concerns linked to the rising use of them.

One of the main risks is that the apps may not be able to accurately predict your fertile window, which increases the chance of unintended pregnancies.

This is because the timing of your fertile window fluctuates greatly. In general, the fertile window is believed to occur in the five days leading up to ovulation, the day of ovulation, and the day after ovulation.

But studies show that the timing of the fertile window can be highly unpredictable, even among women whose cycles are usually regular. In 2000, researchers from the National Institute of Environmental Health Sciences in Durham determined that only around 30% of women see their fertile window fall "entirely within the days of the menstrual cycle identified by clinical guidelines".

"Most women reach their fertile window earlier and others much later," they added.

The unpredictability of fertility windows means that period-tracking apps are often not able to accurately predict them - resulting in unwanted pregnancies, and abortions in some cases.

In the most recent study, which was observational, the researchers wrote: "There appears to have been a significant increase in the proportion of individuals attending Bpas for abortion who use fertility awareness-based methods as a form of contraception and are using no method of contraception.

"This may be a result of preference or it may be related to difficulties with access to more effective methods of contraception in the preconception and post-abortion periods."

The other risk that has been linked to period-tracking apps is data security concerns. In 2023, users became worried about how secure the data they shared was, particularly considering the intimate nature of the data.

Last year, a study by researchers at King’s College London highlighted the privacy and safety issues that beset such apps, which are used by hundreds of millions of people. They found poor data management practices, with the risk of data being leaked or being shared with third parties for advertising or other purposes.

Dr Ruba Abu Salma, lead author of the study, told the BBC: "While female health apps are vital to the management of women’s health worldwide, their benefits are currently being undermined by privacy and safety issues.

"Mismanaging or leaking reproductive health data can lead to dire consequences, with blackmail, discrimination, and violence being among the worst."

Should I use a period-tracking app?

You can use a period-tracking app to help you learn more about your menstrual cycle. They can help you identify pre-menstrual symptoms, anticipate when your next period will be, and help you understand why you may feel differently during the different stages of your cycle.

However, they are not recommended for managing your fertility. The NHS does not officially recommend any period-tracking apps, and warns that natural family planning is not suitable for everyone.

Natural family planning - without the use of hormonal contraception - can be helpful if you cannot use other types of contraception because of a health condition, but it is advised you use other forms of contraception, such as condoms, or abstaining from sex if you do not want to get pregnant.

This type of fertility management may not be suitable for you if:

• you have irregular periods (fertility awareness method)

• you cannot breastfeed (lactational awareness method)

• you need to avoid getting pregnant due to a health condition

• you take a medicine that can affect your baby, such as some medicines for bipolar disorder, migraine and epilepsy

Before you decide how to manage your fertility, you should speak to a doctor or nurse, or ask your midwife for advice.

Read more about fertility and sexual health:

• Why British mums are not surprised by plummeting fertility rates (Yahoo Life UK, 5-min read)

• High cost of fertility treatment causing people to seek help abroad (Women's Health, 2-min read)

• Seven common egg freezing questions, answered by fertility experts (Yahoo Life UK, 6-min read)