Dozens of women have complained after apparently falling pregnant with this contraceptive

In the past, it was common for families to have a lot of children - and there are a number of reasons for this. One of them is that, without the fancy gadgets and technology we have today, there wasn't really that much for people to do with their time other than get jiggy with each other. And that might have been fine if they had a way to ensure against baby-making, but they didn't - which is another reason why mothers sometimes ended up with upwards of 10 kids to feed.

These days, we have condoms and pills and IUDs, all of which are readily available at pretty much any doctor's office or pharmacy. But, back before all that, families had to rely on rudimentary methods of preventing conception, like strange food concoctions or rudimentary 'barrier' methods.

However, it seems that not all of these methods died out, as one of the very oldest forms of birth control has just got a 21st-century upgrade... but it's already proven to be pretty terrible.

Natural Cycles is an app which claims to be just as good as the contraceptive pill when it comes to preventing unwanted pregnancies. It was recently launched in Sweden, and soon attained a great deal of hype - not least of all from the people behind the company.

"It feels incredibly exciting that there is now an approved alternative to conventional pregnancy prevention methods, and that it's possible to replace medication with technology," said Elina Berglund, who co-founded the Natural Cycles fertility-tracking app with her husband.

It works by calculating a person's menstrual cycle, and requires users to input their temperature every day in order to predict when they are most fertile. In theory, it should work, as ovum (egg cells) only live for about a day - so any sexual contact for a brief window of time after that point shouldn't result in a pregnancy.

And, considering all the problems caused by hormone treatments such as the pill or the implant, it seems like a fairly appealing alternative.

Unfortunately, like a lot of primitive contraceptives, it is far from perfect.

The main problem with relying on Natural Cycles for birth control is that menstrual cycles can be altered by a number of factors at almost any given time. Stress, for example, can send the natural bodily functions way out of whack, and any fluctuations in temperature can be easily misinterpreted as an indicator of someone is in their monthly cycle.

What's more, the app gives no protection against STDs, and therefore should only really be used in a committed relationship between people who know they aren't putting their partner at risk by not using protection.

With all this considered, it's perhaps no surprise that 37 of the 668 women who sought an abortion at one of Stockholm’s largest hospitals last year blamed the app for their unwanted pregnancies. And that's just a single location - imagine how many others have also fallen pregnant while using the Natural Cycles.

"An unwanted pregnancy is, of course, very unfortunate and we deeply care every time one of our users becomes pregnant unplanned," the company said in response to the numbers. "As our user base increases, so will the number of unplanned pregnancies coming from Natural Cycles users. This is an arithmetic truth applicable to all contraceptive methods."

They claim the product has a 93 per cent success rate. However, a 7 in 100 chance of getting pregnant is still worryingly high - especially considering there are other contraceptives out there which are more than 99 per cent guaranteed to work.

So, if you're trying to avoid making any babies right now - perhaps steer clear of this method of contraception, too.