Doctor requesting Ultrasound at 38 weeks

I am going to be 38 weeks tomorrow and at my checkup today my doctor said she is sending me to get an ultrasound to check Baby Girl’s size and fluid. Is this normal? A lot of people that I have talked to never had to get an ultrasound this far along. I am quite tiny and they are anticipating a big baby so I didn’t know if that was why to prepare for possible C section. When I was 32 weeks they sent me for an ultrasound to make sure she had flipped and she did so I know she is head down. I also did the NST today and Baby’s heart rate and movement was perfect so I’m just a tad bit concerned. Thanks in advance!