A contraceptive app used by hundreds of thousands of women has been reported to a medical regulator after a number of its customers sought an abortion.

Medics in Stockholm South General Hospital, Sweden, have notified the Swedish Medicines Agency after 37 women, who were using Natural Cycles as a contraceptive, terminated unwanted pregnancies in the last four months of 2017.

Natural Cycles has since said that unwanted pregnancies are an "inevitable reality" of the app, following Swedish reports on the matter.

Natural Cycles costs around £7 per month and claims to be the only certified birth control app in Europe but it is not regulated by the British Medicines and Healthcare Product Regulatory Agency. Women use it, with a thermometer, to input temperature and period data to detect when they are their most - and least - fertile, thus giving the green light for unprotected sex.

Marketed as a hormone-free way to protect from pregnancy, without unpleasant side-effects associated with other contraception, it has become quite popular and has 700,000 active subscribers.