This method isn’t widely used these days, but thanks to some newly created mobile apps, it’s making a come-back (no pun intended).

There are no hormonal changes involved, but the method relies upon you knowing when you’re fertile, and avoiding sex at those times. Apparently, it can be 99 per cent effective, but taking into account human error, can end up being more like 75 per cent effective.

Traditionally, the NHS recommend you speak to a trained fertility awareness professional before beginning, and you’d need to keep a daily record.

However, there is now “an app for that”. Natural Cycles is one such app, that uses an “intelligent algorithm” based on a temperature measurement taken at the start of the day, to predict ovulation and the fertile window.

The app builds a calendar and gives you green days, and red days – when you could get pregnant.

Our initial worry was that some athletic women don’t have regular cycles. What then? Natural Cycles explain that the system takes this into account and creates “a tailor-made solution for each individual.”

They say: “the NaturalCycles algorithm will not yield green (non-fertile) days unless 99.9% certain you are not fertile. To capture your unique cycle pattern from the start, try and answer the questions upon registration to the best of your knowledge. “