Ive used a moisturizing lotion and it seems to be working as im 8mths pregnant and don't have any strech marks as all
Seriously drink a bunch of water, and OIL your tummy twice a day.
Stretch marks are caused by your skins elasticity... Which is genetic. But keeping hydrated will help A LOT and find a lotion/oil/cream and use it everyday if not twice a day. If you get itchy don't scratch! Put lotion on. I use bio oil (kinda expensive) but it's recommended by lots of people and I love it.
I used bio oil, stretch mark cream and cocoa butter almost every night after I showered and still got stretch marks,... there isn't really alot to completely avoid them, but keeping your skin hydrated can help with the appearance.