Most women gain a little in pregnancy, but most don't keep a lot of it. Some gain more if they are home for long with baby/toddler. Some gain more with second or later pregnancies. Often the fatter going in, the less the gain, from what I understand.
In short: congratulations, you two are going to have a baby! Get ready for your life to get totally changed around. And try to enjoy the changes, BUT don't count on any particular change.
And good luck