Hi kas

Babies can put on anything between 1kg and 1.5kg a month.
I am a little confused as to how your your Dr can be so accurate with your babies weight. I have seen on many occasions where mum has been told that she is having a small/large baby only to find out this is not true. A few weeks ago a woman under my care was told by her Dr that her baby is going to be well over 9 pounds. He was 7pounds 4oz when born at 41 weeks.
Dont stress you hun. Talk to your Dr at your next visit. Ask him how he can be sure of the babies weight.