AN investigation has been launched into a contraceptive app which was linked to 37 unwanted pregnancies.

The Advertising Standards Authority (ASA) said it was probing a paid-for Facebook post.

The watchdog said the app had described itself as a “highly accurate, certified, contraceptive app that adapts to every woman’s unique menstrual cycle.”

The ASA has received three complaints about the social media post, alleging the claims to be misleading and that they cannot be substantiated.

The watchdog said it had yet to make a decision in the case and would publish the findings of its formal investigation "in due course".

The app's co-founder Raoul Scherwitzl said: "We are in contact with the ASA regarding the case that has been ongoing for nearly one year now. The Facebook advertisement in question ran for a short period of time in 2017 and has since been taken out of circulation.

"We can confirm that every ad undergoes a strict approval process, which requires that the claims made are backed by clinical evidence.

"The effectiveness of Natural Cycles is supported by clinical evidence and our certification has been granted based on mandatory clinical data."

In January the app was forced to defend its technology after being linked to 37 unwanted pregnancies.

According to a report in Sweden - where the company is based - at least 37 women have become pregnant while using the app, which has led to the country's Medicines Agency being notified by one hospital.

In response to that, Natural Cycles said cases of unwanted pregnancy are an "inevitable reality" with any form of contraception, not just their app.

Natural Cycles uses a thermometer, linked smartphone app and machine learning algorithms to determine when a woman is fertile.

Last year it was certified in the EU as a medical device intended to be used for contraception, and the app markets itself as a viable alternative to the pill and other hormonal treatments because it lacks the side effects.