Before we made our choice, I did tons of research on doppler vs ultrasound, and actually a minute with the doppler is equivalent to an hour of u/s. Doppler is much more concentrated and a continuous stream, rather than intermittent like u/s.
Because our first son had a heart defect we chose to do a high level u/s at 22 weeks to see if this one would have a healthy heart. I am so glad we did, but that was our only u/s, since really, it doesn't change the outcome, it only lets you know what is going on.
We'll use a fetoscope the rest of the time if we need to hear the HB or anything like that.
(I'm an August Mama, not Jan, so I'm further along than you lovely Goddesses are, but I had to chime in since we really did worry about and research this as much as we could.)
Happy pregnancies, lovely glowing ladies!