An Australian study of the most downloaded fertility apps has found over half didn't perform well at predicting ovulation — which is exactly what many users are using these apps for.
Less than half of the apps studied predicted the correct ovulation date
Relying solely on an app to avoid pregnancy is a risky game
Apps that take temperature data or urine tests are more likely to be reliable
The findings, by researchers at Eve Health Fertility in Brisbane in conjunction with Queensland Fertility Group, were presented at a Fertility Society of Australia conference this week in Hobart.
The researchers found that between December 2018 and February 2019 there were nearly 400 fertility apps available for Australian women. They analysed the 36 most downloaded of them, which were all on both iTunes and Google Play and in English.
Less than half (42.7 per cent) predicted the correct ovulation date and fewer than one in five (17.1 per cent) predicted the correct estimated due date of a baby, the researchers report.
Many apps also gave incorrect timing for intercourse and incorrect fertile-window calculations.
There was also a "disturbing" lack of reference to scientific evidence — with less than 10 per cent providing references for claims, said researcher Samantha Costa.
But while many of these apps may not be effective, they are wildly popular.
Among adults, they're the fourth most downloaded type of health app and, among adolescents, that ranking jumps to second, Ms Costa said.
"At least 70 per cent of women that are going through some form of fertility treatment rely on these apps to track their cycles," she said.
"And that's really how this study came about — on a daily basis, we asked patients 'do you know where you are in your cycle, do you know whether you ovulate?' And the common theme there is 'let me just check my phone. Let me just check my app'.
"So they are very, very reliant on these applications."
According to Ms Costa, all the apps in this space market themselves as a means of being able to track the menstrual cycle and help with planning fertility. But a lot of them also market themselves as a contraception tool, so it's important that they are reliable.
Ms Costa said the study showed these apps and the claims they made needed to be reviewed by an expert body so consumers knew which they could trust.
What to look for in a fertility app
Figuring out which fertility apps are most reliable isn't as easy as listing them in league table form, because apps come and go, and change as software is updated.
But there are some clues you can look for to help you pick the winners from the duds, according to Robert Norman from the University of Adelaide.
In general, the apps that asked for the most information were the most reliable, said Professor Norman, who was not involved in the study.
In addition to tracking the days of your period, some apps ask users to take their temperature or use urine tests, and these are the best apps.
"The best ones need something added — a thermometer or urine sticks. Just going on a tracker alone is inadequate," he said.
But at the very least, get an app that asks for the length of your menstrual cycle, Ms Costa advised.
"Some of the applications didn't even ask for a cycle length, so they were predicting a cycle based on a 28-day cycle and we know that not everyone has a 28-day textbook cycle," she said.
Relying solely on an app to avoid pregnancy was a risky game, said Kathleen McNamee, fertility expert at Monash University and medical director at Family Planning Victoria, who was not involved in the study.
"We try and talk people out of fertility apps because it's hard to stick to the rules," Dr McNamee said.
"Some may be as good as the pill but you have to be highly motivated to do it properly."
The reliability of the app you use also depends on how you use it.
Entering information into your app in a timely way will help make it more accurate. It's also important to be consistent in how you define things like the first day of your period.
Fertility-tracker apps were valuable because they helped people tune into what was happening in their bodies, Professor Norman said.
"There is a high proportion of women who really don't have very much clue about when they're ovulating and an app may put them in to the ballpark of when they should be thinking about ovulating," he said.
"So they largely have an educational role these apps rather than a predictive role."
But he echoed Ms Costa's warning to check out an app's features before downloading.
"Like with all apps, there are some that are based on very sound science with good research behind them. And then there are others that are highly opportunistic, that are just taking money off people and not really based on anything that's substantially different from what people really know themselves," Professor Norman said.
Apps are a data source, for better or worse
Researchers like Professor Norman collect anonymous research data from apps like this to understand menstrual cycles better, and this kind of research can also help to make apps better.
But he says people need to be aware of where their highly private data entered into the apps — on periods or sexual activity, for example — is going to end up, and whether they will be identified.
"Most people don't want people to know when they're having sex or not having sex," Professor Norman said.
"If you knew that one of the film stars was only having sex once every three months then that would be quite newsworthy."
Ms Costa said one of the apps reviewed had an eight-page-long privacy clause that people were unlikely to read, but allowed data to be handed over to a big health insurance company in the US.
"I think the consumer needs to have that clearly stated and not within the fine print but within the information that they get when they look at the initial download screen for an app."