Could someone please let me know what is normal for the baby's heart rate.

Because at 9 weeks 4 days the heart rate was 183 and at my 12 week check it was only 122 both times I was told this was normal but I had two different sonographer's. Just wandering if it's normal for the heart rate to vary so much or should I check with my OB?

Hope someone can help me out ?

Thanks,
xxdd