While there are hundreds of products claiming to prevent stretchmarks, the truth is that the biggest factor in who gets stretch marks and who doesn't is genetics. If a woman's mother had them during pregnancy, it is likely she will as well.
Skin type plays an important part in why some women get stretch marks and other don't. Another factor is how much weight is gained during the pregnancy. A little weight gain equals less stretching of the skin versus a large weight gain which really stretches it out. Some take better care of their skin and apply creams which really helps.