Ultrasound vs uterus measurement

So I have gestational diabetes, I’m 33 weeks and 3 days and was told baby is very large. He was measuring 3 and a half weeks ahead. So they sent me to a High risk specialist to do a baseline ultrasound yesterday. Ultrasound tech and specialist said baby looks good he’s only measuring a week ahead and weighs around 5lbs 3 oz and everything looks perfect for being a GD baby. Well today I went to my regular OBGYN and she said my uterus is Measuring 37 weeks! So what’s more accurate ultrasound or my doctors measurements? I’m so confused!