InVivo - I'm the opposite way around, last pregnancy my starting BMI was 42 and I barely gained anything, about half a stone in third trimester. I wasn't particularly trying, but I monitored my weight and made an effort not to eat any more than I usually did.
I've been going to SlimmingWorld for a year and my starting BMI this time was 37, and I'm hoping to maybe have a small gain in first tri (hopefully no more than I already have!!!) then maybe a similar gain in third tri. Maybe a 14-20lb maximum? I'm not too worried as I know I can get it off after, and eating healthily is more important to me. Plus I saw a documentary a couple of years ago where they had found that the biggest indicator for childhood obesity was not enough calories pre-natally, which I know is unlikely, but seems a good reason to relax.
I think I was just shocked as it was so easy last time!! lol