Babies belly measuring big

I had an ultrasound today at 30w2d and baby's measurements were all fine except the tech said his belly was measuring too big. I haven't got the results back yet from glucose test but she said gestational diabetes could be one cause of it. I have to go back for another ultrasound in 4 weeks because of this. Has anyone else been told this before? Baby was measuring 3Ib 15oz and 15.9 inches.