I was 63kg when I fell pregnant and put on 12kg thruout my pregnancy. When I left hospital 3 days later I had lost 10kg already!!! Now 4 months later I am back to my original 63kg!
I was however always a lean built girl......Don't worry about what you gain tho unless it is excessive as that can be dangerous! That's why you will never be weighed by your caregiver throughout your pregnancy as it is not an issue!