S.,
Strech marks have more to do with the collagen content in your skin and sometimes it is unavoidable. If you already have them, you can't really get rid of them. All you can do is minimize the number of new ones that appear.
One thing is for sure, it's not only what you put ON your body as much as it is what you put IN your body. Make sure you have a healthy diet and take your prenatal vitamins and most definitely drink a LOT of water. I am at week 37 and have no stretch marks. Part of this is genetics (my mother never got them) and the rest is due to the never empty glass of water I always have. Sure you pee alot, but it's the best thing for you and your baby.
Another benefit from drinking lots of water is that you will actually have LESS water-retention than if you aren't well hydrated. Salt's also a culprit in water retention and you will be more sensitive to slat when you are pregnant. So avoid the chips and french fries if you can.
Good luck!
N.