My normal weight before I got pregnant was 98 lbs. for years. And I drank whole milk, ate real icecream and real cheeses. Never touched the 'diet' foods.
When I got pregnant I took my prenatal vitamins and iron and still ate normally. It is my opinion that if you want a baby, a healthy baby, whole milk and real cheese is better for development. And it's still the best while nursing.
I weighed 150 lbs when I went in to deliver, after delivery I weighed 130 lbs. and it took me two years to get back to size 7 and then 5. But it was worth it because I had a healthy baby and nursed for 14 months. I made my choice - I wanted a baby, and wanted a healthy one - that was my priority.
Later after that was achieved, I danced, swam, exercised to music, and got back to my 'sexy' stage and had fun sewing new clothes for myself and felt great.
So, it all depends what your priorities are and how to achieve them. I don't regret the big bum or big boobs - that was nourishment that nature meant for my child and after that I could do what I wanted again. I never let 'society' tell me what weight I should have and how I should look, I did not need to look like 'Twiggy' at any time in my life and still felt like a sexy woman. It's mostlly in the mind - IMO...
So,, you ladies that want to stay skinny all your life, either don't have kids or get some other woman to have them for you.. but you'll miss out on the most wonderful feeling and pride in seeing that sacrifice grow to hug and love you for being just you, no matter whether you are heavy or skinny.
Just had to put my two-cents worth in, I hope I did not upset any of you, that was not my purpose here.
Motherhood is the hardest job in the world, but worth every effort!

A happy and proud Grandma!