Fetal heart rates

Hi guys! Just went to a 14 week OB appt and we’re pregnant with twins! At 9 weeks their heart rates were in the 170s, but today they were 153 and 120-125 range. Is 120 too low for 14 weeks? All the articles I’ve found online refer to 6 week/9 week fetal heart rate and predicted health of the fetus but for some reason 120 just seems sort of low to me? The dr didn’t say anything but I’m just anxious these days with a twin pregnancy.