A fertility app for smartphones that analyses a woman's temperature and ovulation tests in order to identify fertile days is as effective a contraceptive as the pill, according to new clinical research.

The Natural Cycles app creates an algorithm based on a woman's temperature when taken each morning to build a data plan of fertility - showing the days on which a woman could get pregnant. It then notifies users to take precautions on fertile days in order to avoid the risk of pregnancy.

Now, a clinical trial based in Sweden involving more than 4,000 women aged between 20 and 35 has found the app to be as effective as a form of birth control as the contraceptive pill.

According to the research, which has been published in the European Journal of Contraception and Reproductive Health Care, Natural Cycles scored similar results to the pill on what is known as the Pearl Index, which measures the effectiveness of birth control methods by measuring how many subjects out of 100 will experience an accidental pregnancy within the first year of use.

While the pill has a Pearl Index score of 0.3 - meaning that around three women in 1,000 who use the pill "perfectly" experience an accidental pregnancy - the Natural Cycles' system has a Pearl Index rating of 0.5, according to the study.

Another previous study found the app to only falsely predict non-fertile days 0.05% of the time.

Dr Elina Berglund, one of the app's creators and a physicist who was part of the team that discovered the Higgs boson particle, said: "Mobile technology is the most transformative trend for healthcare in recent years.

"Natural Cycles uses data instead of chemicals to prevent pregnancies thereby allowing women to educate and empower themselves and take control of their fertility. The future of birth control lies in knowing your body rather than altering it with hormonal contraceptives, and we are excited to be leading the way and creating a future where every pregnancy is wanted."

Professor Kristina Gemzell, one of the authors of the study, added: "More and more women, especially in the age group of 20-30, tend to abstain from hormonal contraception and desire a 'hormone-free' alternative. It is important to increase choice among contraceptives for women and inform them about their pros and cons.

"Studies on natural family planning have been scarce and actually non-existent for any mobile applications - this work is an important step towards understanding how new technologies can improve old methods."

Natural Cycles also confirmed that the app, which is already available and free to download, will now be part of further clinical studies in which it will be directly compared with the pill.