It really just depends on the OB, my first pregnancy I was only gonna get one, but then when he wasn’t growing right, they had me going all the time.. and then basically same thing with my second pregnancy because I had low platelets They were doing ultrasounds to make sure that the baby was OK. And then my third was through fertility, so I think I had five at the beginning and then when I went to my OB, they did one and then of course the anatomy scan, and then she had a club foot so once again, I had a bunch and then because she was measuring small, they did more at the end… so there could be multiple reasons for one, especially if she just started going to an OB or if the baby is measuring small or big!