Measuring ahead!

Braidy

So I went in for my last appointment at 29+4 and my doc measured my belly and said I was measuring a bit ahead at 30. I didn't really think much of it but she seemed a little concerned. It's bugging the shit out of me so what I'm wondering is why was she so concerned about me measuring a bit ahead? Probably a stupid question but it's been bugging me for a week now!