Mine is usually in the high 160's and my last appt it was in the low 130's. Totally normal
I guess if your doctor is not concerned, everything is okay.
Incidentally, at my visit today, the midwife said, "150, that's high for a boy." And I thought, Oh? So the "old wives' tales IS true!? Then she said he was moving around, so that made it higher.
I'll bet darkestlight is right, the baby was probably sleeping.
A normal fetal heart rate is between 120-180 depending on activity. your baby could have been sleeping.
My OB never tells me what the heart rate is, I suppose I could ask but I assume it is fine if he doesn't say anything......
Babies heart beats go up and down a lot depending on how active they are at that moment. If your dr says it is fine I would trust her.