The chip is 2cm-square and seven millimetres thick, and will go into clinical testing next year. It delivers a daily dose of 30mg of levonorgestrel, which is already widely used.

If and when a woman wants to conceive, she can use a remote control to temporarily turn the chip off. The chip has been created by a company called MicroCHIPS, based in Massachusetts.

Inside the chip is a reservoir which contains and protects the hormone. A minute electrical current from a small internal battery causes the chip to release each dose.

A local anaesthetic is used to implant the chip, and the procedure takes around 30 minutes. If the contraceptive chip works, potentially any drug could be placed in the reservoir to be released on demand or on a set schedule.

Pre-clinical trials – backed by the Bill and Melinda Gates Foundation – will begin next year. It could be on the market by 2018.