Bird's do not get pregnant like mammals do. If your bird has a distended belly, they need immediate medical treatment. If you mean 'egg laying parakeet' then providing her with lots of protein, fresh water and nutrients as well as quiet is best for her.
pregnant parakeets must have a cool atmosphere and any food like egg,papaya and mango should be avoided as it may heat up her body, all kinds of other fruits can be given. boiled vegetables like carrot,beans,greens can be added to her diet,which will increase her stamina and serves as nutritious food.