Undortunately there isn't anything you can really do to prevent them.. Keep moisturised, drink plenty of water and try not to gain to much excess weight is all you can do to try to help, but if your going to get them then unfortunately they will come!
Lotions will not prevent stretch marks. The biggest thing I was told is that if you eat healthy and don't gain excessive weight at one time that will help not get them. With my first pregnancy I used a bottle and a half of cocoa butter and still got stretch marks. It because I gained weight so fast in a small amount of time that my skin had to stretch so far in so little time.
I had none up until 32wks and now I am 34wks and sides of my belly are covered. I used Bio Oil but if you are going to get them you will get them.
I use coco butter and I have no stretch marks! But my friend went through her pregnancy with no stretch marks and when she had her baby and her stomach flattened she had some :/