Can a Fitbit really tell if you're pregnant?

But within weeks, Ivonne's Fitbit started recording her resting heart rate at a high range – sometimes up to 110 beats per minute (bpm) – which was much higher than it normally was.

Most adults have a resting heart rate of 60bpm to 100 bpm but, the fitter you are, the lower your resting heart rate is likely to be. So a top athlete like Jessica Ennis-Hill might have a resting heart rate of 40-60 bpm or lower.

A faulty Fitbit?

Anyway, after such a whopping difference from her normal heart rate, Ivonne assumed her new device was faulty and asked David to take a look.

He posted about the problem on a Reddit forum for users of the trendy wearable fitness tracker.

"My wife's Fitbit is showing her heartbeat being consistently high over the last few days," the posted. "Two days ago, a somewhat normal day, she logged 10 hours in the fat-burning zone, which I would think to be impossible based on her activity level.

"Also her calories burned do seem accurate. I would imagine if she was in the fat-burning zone, she would have burned a ton of calories, so it's not lining up..

"I'm not sure if something is wrong with the sensor. Is there a way to reset or recalibrate the device? I'd like to try that before I contact customer service about a possible replacement."

Lots of helpful people wrote back but one Reddit user's comment in particular caught David's eye.

"Has she experienced anything really stressful in the last few days or is it a possibility she is pregnant?" it read.

David was shocked – but told Ivonne anyway.

She took a pregnancy test and it came back positive. Hoorah!

Did the Fitbit really detect Ivonne's pregnancy?

We asked our expert family GP Philippa Kaye if tracking a higher heart rate can really reveal if you're pregnant. She told us that it's true that a higher heart rate is experienced by all women when they're pregnant, but unless you're using a heart rate monitor, you just won't notice.

"During the 1st trimester, there is a slight increase in heart rate as well as a slight rise in temperature," she says.

"Ivonne did noticed her heart rate increasing because it went above 100, which is quite high. But if you are very fit and active and have a low resting heart rate – 65, say – then even a 10% increase would only bring your heart rate up to 72 bpm which is still well within the normal range, so you may not notice it."

When can you expect to experience a rise in heart rate?

"Some women will be aware of an increased pulse rate from the 1st trimester; others won't notice it until the 3rd trimester and some women may not be aware of it at all," says Dr Philippa.

"Some women may experience palpitations: an awareness of a fast or irregular heartbeat during pregnancy."

Should you use change in heart rate as an early sign of pregnancy?

"Not really as it is so variable!" says Dr Philippa. "If you are someone who regularly monitors your heart rate, you may notice a change but this change could be for a variety of other reasons. Even the caffeine from drinking a cup of coffee can affect it!

"I advise waiting until your period is due, or overdue, and then taking a pregnancy test for a more consistent result regarding whether or not you are pregnant.

"Other symptoms of pregnancy in the 1st trimester include needing to wee more frequently than normal, fatigue (or more often exhaustion!), tender breasts and nausea with or without vomiting.

"However, some women may experience all of these symptoms and others none at all. Whether or not you have these symptoms gives no indication about the pregnancy itself, so try not to worry!"

Pics: Getty Images

Read more:

• Early signs and pregnancy symptoms
• No period but negative pregnancy test - why you could still be pregnant
• False positive pregnancy test - is it possible?