Stretch mark creams do not work. The "stretching" comes from the deep layers in the skin and not on top. Moisturizing isn't going to stop it. It's mainly hereditary if you are going to get them.
As soon as your baby is born and you are not breastfeeding, get some Retin A from your doctor. It is the only cream/medication proven to lessen the severity of them but it must be applied while they are still new and reddish.