A contraceptive app which uses body temperature to track a woman's menstrual cycle is 93 per cent effective, a landmark study has found.
The findings, based on 22,785 women, even show Natural Cycles works slightly better than the Pill in preventing pregnancies.
The smartphone app, which is approved in the EU as a contraceptive, predicts the days of the month when a woman is most fertile.
On these, which are called red days, it advises couples use a condom to reduce the risk of an accidental pregnancy.
Since its inception in 2014, its manufacturers have claimed it to have a 93 per cent effectiveness rate. However, the trials were based on much smaller groups.
The findings, based on 22,785 women, even showed Natural Cycles works slightly better than the Pill in preventing pregnancies
Professor Kristina Gemzell Danielsson, based at the Karolinska Institutet, Sweden, was behind the results - which are the largest of its kind.
She said: 'Since more and more women are choosing natural contraception as an option, we welcome that there is a certified app with solid clinical evidence.'
'It shows the app is effective'
Dr James Trussell, based at Princeton University, New Jersey, also welcomed the research published in the journal Contraception.
He said: 'This is the first study to provide typical and perfect-use estimates of effectiveness of an app and shows the app is effective.'
Participants involved in the study had an average age of 29. Nearly 7 per cent went onto become pregnant.
The Pill is known to have 91 per cent effectiveness in preventing pregnancies. Other methods can be as low as 75 per cent.
Dr Raoul Scherwitzl, co-founder of the app said the results 'confirm the effectiveness of Natural Cycles, which is used by 380,000 people worldwide.
Women 'shouldn't rely' on a smartphone app designed to track their menstrual cycles, fertility experts claimed in July.
Studies have even found Natural Cycles, which plots ovulation on a calendar, to be as effective in preventing pregnancies as the Pill.
But it's unreliable, says Dr Mary Jane Minkin, a professor of obstetrics, gynaecology and reproductive sciences at Yale