Normal fetal heart rate progression?

First time mom here. 16 weeks on Saturday. Just got through with my second nurse practitioner app. She had to chase baby to get a good hb haha. Anyway hb was 140 which I was told was really healthy and normal. But it worried me because it's dropped so much. My first 8 week scan hb was 175, then second app at 11 weeks was 161, then this one was 140. I was curious if this sounded like a good normal progression. I wasn't sure what a normal progression was. I know I shouldn't be worried and I'm not really. Especially since nurse was super happy with it.