I was only weighed at the first appointment. (Thank goodness!)
I went from 9st 2 to 8st 7 in the nausea phase when I could barely eat, then up to 13st by 39 weeks. It was mostly bump- 8lb10 of baby and a lot of fluid. I'm short, so there was only one place for it to go! My waist went from 27 to 43 inches, and the fundus measurement went to 45 cm!
There was about 1.5 stones of "me" weight to lose after the water retention etc had gone, and I've settled at a lighter weight than my pre-pregnancy weight.
I think my gains were for a few reasons; I'm normally active but the nausea/ exhaustion phase was followed immediately by SPD so I was very sedentary through most of the pregnancy. I think the nausea combined with being sedentary could have affected my metabolic rate and slowed it down compared to usual. In the late stages, I was exhausted from constant pain, so craved quick release carbs. Snacking was also one of the few forms of entertainment I could manage!
I did have a couple of extra scans due to the rate of bump growth which rocketed well off the graphs. By week 38, the MW concluded that it was my "normal" having had a scan the previous week. Weight was never mentioned. I kept my waist until late on- people were frequently surprised when I turned around and revealed my swiss ball bump after my slim rear view. 
My legs struggled with the weight and I was near housebound in the final month. Second time, I managed to stay a stone lighter. I scrounged crutches to keep active, and controlled my sweet tooth better. I think the main difference was water retention as the "me" weight to lose after was the same.
I've heard that smaller people are more inclined to lay down reserves during pregnancy. It was certainly obvious on me anyway!
It's only recently that my 3&5 yo's combined with my weight have exceeded my pregnancy weight! No wonder my legs were buckling!