measuring behind

Lindsay
So I went for my weekly appointment at 37+3 today and the doctor was feeling around to check baby's position. She says, "whoa, you have kind of a small baby there!" So I ask her what she means and she measures my stomach and says my tummy is also measuring behind. Mind you, This is the first time I've had anything unusual at any appointment throughout my whole pregnancy. I'm pretty tiny myself (5'1" on a good day) and my husband is on the shorter side as well. We were both born at 6lbs 9 oz. She did acknowledge that my daughter could just be small because we are small, but still. 
long story short the doctor has us scheduled for a growth ultrasound next Monday to check it out. I just find it odd that she's measuring behind all of a sudden because I gained 2lbs since last week. I did some reasearch and it seems like common practice is to induce early (38 weeks) if baby isn't growing at this point in the game.   Anyone have experience with this happening to them? How far behind would she have to be for them to induce me?