Heart rate question?

Britt • 👦🏼💙 May 27, 2016 ;👼🏼 12weeks Nov 2017 ; 🌈 💙🧒🏼March 8, 2020 💖👶🏻 Aug 3, 2021
On Wednesday I went to the Dr. And we were able to hear the heartbeat with a Doppler. The dr said the heart rate was about 155-160. Yesterday we went for my 12week scan and everything looked great but they measured the heart rate at 140 (not with a Doppler just with the U/s screen) Is it normal to drop so much in 2 days?