An investigation has been launched into a contraceptive app's accuracy after it was the subject of complaints.
The Advertising Standards Authority (ASA) said it was probing a paid-for Facebook post in relation to the Natural Cycles app.
Natural Cycles uses a thermometer 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.
The watchdog said the app had described itself as a "highly accurate, certified, contraceptive app that adapts to every woman's unique menstrual cycle" and said it is a "clinically-tested alternative to birth control methods".
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".
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 - the women became pregnant while using the app, which has led to the country's Medicines Agency being notified by one hospital.
In response, Natural Cycles said cases of unwanted pregnancy are an "inevitable reality" with any form of contraception, not just their app.
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