I think my Dr only does 2. I had one at the hospital during a screen for down syndrome but other than that I've had to go to a boutique

I had one at 12 weeks 3 days, and one at 18 weeks 3 days. My midwife wanted to do the minimum, she would have done another if complications came up though

I had one at 12 weeks, another at 20 weeks and I go in tomorrow for another so we can see how big baby boy is.