That's happening to me right now. I've been measuring 2-3 weeks ahead my last 3 appointments. I haven't gained a lot, 13 pounds so far. I think excessive weight gain can cause you to measure ahead. This is my third and only baby that has measured ahead. My midwife isn't worried. She said it could be the babies position, or partially because my uterus has been more stretched out since this isn't my first pregnancy. My sugars are also higher than normal, but not in the gestational diabetes range. She said he could be a bit bigger because of that. My other two were 8 lbs 1 oz, and 8 lbs 11 oz.