Hey.
There are lots of factors that determine how much weight you will gain during pregnancy and what you eat is just one of them. Your age, race, height and pre-pregnancy weight all influence how your body is going to change whilst being pregnant. The one thing you can be sure of is that you will put on weight. well hopefully!

With my first son i started at 72 dropped to 65 (due to bad morning sickness) then at birth i weighed 78, two days later i weighed 63...
This time round i started off at 74 and at 25 weeks Ive only put on 3 kilos so far... but alot of ppl say that you put on the most kg's in the last trimester.
As long as your eating healthy and nutritious food and doing some light exercise.
Last time i lost the baby weight that day i think mostly due to fluid. remember not all the weight you put on is just baby and fat.. the placenta, your blood volume increases, amniotic fluid ect, all this contributes to your weight gain.