Since he was not your regular doctor, I would take what he said with a grain of salt. You have to remember that the tape measure test really isnt as reliable as an ultrasound test, which isnt 100% either. He was probably just warning you. Your regular doctor will know what is going on, trust me, you did not suddenly pop out in a snap. If your regular doctor was concerned, she would have said something by now. Doctors dont want to get into trouble for not warning a person, however, because of this, I think they put too much stress on us all by being overly careful. For example, my baby needed an MRI for a surgery on her eye. When she was born, she had some breathing problems, which caused her to be sent home on oxygen, and she stayed on it for only 3 months and her lung doctor said to never worry about it again. Now I had to tell the MRI people about it, and they freaked out. I had to reschedule this test 5 TIMES before I finally had to have my regular doctor step in and basically force them to do it. We got sent home once because she had a slightly runny nose, and the next week they tried too again, but my doctor helped me out. So you see, not all doctors know what is going on. She not only flew thru the sleep meds for the MRI, but had a successful surgery on her eye too!!! Talk to your regular doctor before scheduling an Ultrasound, because she really will know you best and your history of big babies too and will know when to be concerned. Good Luck and Congratulations!!
PS according to the ultrasound, my baby was going to be 9lbs 9 oz, but instead I delivered a beautiful 8lb 13 oz little girl ;)