Every person is different, but I had a net weight loss with 3 of my four pregnancies, and the one in which I had a net gain was actually the one that set me down the path of morbid obesity. 3 of the 4 babies were huge. I had healthy pregnancies with no problems and normal deliveries.
Pregnancy 1: start weight 196, high weight 231, post-baby 231 baby weight 9.6
Pregnancy 2: start weight 276: high weight 276 post-baby 250 baby weight 10.6
Pregnancy 3: start weight 250: high weight 250 post-baby 230 baby weight 8.0 (I should add that I really watched what I ate this time-- didn't want another 10 lb baby.)
Pregnancy 4: start weight 275: high weight 275 post-baby 250 baby weight 9.10
Success consists of going from failure to failure without loss of enthusiasm.--Winston Churchill