20 weeks measuring ahead, anyone else?

Tanya

I saw my MFM on Tuesday at 20 weeks amd u/s looked good, she was measuring 5 days ahead, arms and legs were measuring long and she was about 13oz. Today I had my appointment with regular OB and my uterus was measuring 2 weeks ahead. Slightly nervous about having a big baby, I have a smaller frame and haven't gained too much weight. Anyone else in a similar situation?