My doctor said that her patients with PCOS typically do not gain much weight with pregnancy?

I am seeing a weightloss doctor, and she told me yesterday when I was asking about getting pregnant, that her patients with PCOS typically do not gain much weight during pregnancy, and she doesn't know why. Is this true?

Sometimes I feel like she basically knows nothing about PCOS and is very nonchalant about a lot of things. She told me also not to worry about gestational diabetes because sometimes it happens, and sometimes it doesn't haha.