It is very low for 7 weeks, but could they be off in gestation? Did he say the fetal development was right for 7 weeks. When they can very first find the HB on u/s (sometimes as early as around 5 weeks) you can have very low fetal heart rates & have it still be normal. It increases by about 3 beats a day I think until it gets quite high...but it starts off pretty low. Again though, by 7 weeks you are talking over 100 usually.