Heart rate

I’m not sure if I should be concerned, although my ultrasound tech said I shouldn’t be. My babies heart rate has always been between 160-170 and she was never said to be growing off track by more than a week

My last ultrasound her heart rate was 143 and the ultrasound tech said she was “skinny around the stomach” and that she was weighing ab 2.13 oz

I’m 31 weeks tmr and have an appt in the morning so hopefully I’ll get some more news. Just wondering if anyone else has experienced this and could give me some input or insight?