I'm so glad I stumbled across this thread - I have read passing comments about the questionable safety/necessity of ultrasounds but I've never read about any proper, randomised studies until now (thanks Alan!!).
So interesting to read that u/s made no difference in outcome for high risk babies.

I had just the 1 18-20 week scan with DD but this time - being twins, I have had several quick scans which I'm not altogether comfortable with but it seems to be common practice with twins. I am trying to avoid unnecessary u/s but it's quite difficult to do with a private OB.

I understand the doppler they use to hear h/b is similar technology to u/s. My question is: Does anyone know how they differ - what is the difference in strength of the sound waves etc? I guess really frequent u/s is unusual unless there are high risks but regular checks with the doppler are common.

I guess I will go and do some google research about doppler and u/s technology...