I don't believe you can't prevent stretch marks per say but by using lotions twice daily, drinking recommended daily water intake and eating lots of greens you should be able to prevent how bad they can get. The lotions and water help to hydrate your skin and lots of greens help with the elasticity of your skin.
Some women are lucky and dont get them at all, other women can be covered in them regardless of what they do. It's generally around 30+ weeks that stretch marks will start to appear because that's when most women "pop".
Do NOT use Palmers lotion. It makes you so itchy. & I didn't have any till I used it! The very first time
Rub coconut oil with vitamin e on all the place you may possibly get stretch marks. It may not keep you from getting any at all, but it will keep you from getting alot of bad ones. And will greatly reduce the appearance of ones you may already have.
Avoid scratching your belly, that causes stretch marks.