My three kids all have the same parents and were all born at around 39 and a half weeks (can't remember exactly!).

DD1 - 2.7kg
DS - 3.57kg
DD2 - 3.30kg

I ate the same diet with each of them and did not have GD with any of them. I gained around 12kgs during each pg. DD1 is still on the small side, she is now 10 and weighs 26kg. I think she is just made little, we come in all shapes and sizes and she is small. I am certain of her dates, she was not early. I agree with the PP who said that a bigger baby is easier! DD1 was jaundiced, sleepy, difficult to feed and had a poor sucking reflex. Everyone from the MCHN to the paed hassled me about her slow weight gain. The other two were better feeders and seemed more robust. DD1 was also the most difficult delivery by far.