i had one at 15 weeks, then 22, then again at 30 where they were afraid i was low on amniotic fluid, i never was but they wanted to make sure so i didn't complain. after that i got one every 2 weeks after 30 weeks, so 30, 32, 34, 36, 38. but that's not necessarily normal.

I only had one at 8 weeks and 20 weeks :( wish I could have had another one