I had my doctors appointment today, I will be 37 weeks on Sunday. My doctor wants me to have a follow up ultrasound because she said I am measuring small. I was measuring fine up until this point.

I asked her if I should be worried and she said no, that her head might just have moved into the pelvic area. But I am still worried. Has anyone had this happen? Anyone measuring small?? I have gained 16 lbs so far.Please help!