From what I understand, a lot of what determines if women get stretch marks is genetics. If your mom and sisters (and your mom's sisters) have stretch marks, I've heard it's a good bet you'll get them, too.
I'm sure water consumption plays a part too, and I have heard of women who got no stretch marks on places where they used belly oils or creams, and did get them on places they neglected to put them, so obviously, genetics aren't the only factor. (A friend of mine used a belly oil on her tummy for the whole 9 months, and got no stretch marks there. However, she didn't even think of putting the oil on her breasts, and therefore ended up with zebra boobs! :LOL)
I've also heard (don't remember where I read this, it was during my last pg, so don't quote me or anything! :LOL) that the women who don't get stretch marks are also the least likely to tear during birth. Something about how if the skin is stretchy enough to stretch over a growing belly without getting stretch marks, it means the perineum is stretchy, too. So, if a woman has a lot of stretch marks, she could be more likely to tear during birth. So far it holds true in my family - none of the women (including myself) have any stretch marks or tore during any delivery. My zebra-boobed friend tore significantly.