Three days ago, Reddit user YoungPTone posted to the site's Fitbit forum asking for some advice on his wife's fitness tracker, writing that it had been "showing her heartbeat (as) being consistently high over the last few days".
"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," he wrote.
"Also her calories burned do seem accurate. I would imagine if she was in the fat burning zone she would burn a ton of calories, so its not lining up."
He wondered if there was something wrong with the calibration of the device but one commenter suggested a different possible reason - could she be pregnant?
YoungPTone said that that was "a strong possibility" and joked, "I might be a dad, YIKES. Now I gotta watch my own heart rate lol."
He went off to inform his wife and, a day later, came back with an update.
The Redditor who called it correctly said she had a hunch as she recently had posted a graph showing how her heartrate had changed after becoming pregnant.
How getting pregnant affects resting heart rate.