10 weeks but heart rate is different.

Katmom ~

My ultrasound tech and Dr didn't seem concerned but I am just wondering if this is normal to have heart rate of the baby changes on US?

Last weeks ultra sound baby's heart rate measured 178 and today 10 weeks and 2 days heart rate was 167bpm.

Is it normal ? Every ultra sound I had the heart rate kept going up but this time it went down a bit.