I use the body shop's coco butter from early on right through and at the end of the day it didn't help... I stil ended up with strech marks.... Maybe I didn't get as many as I would have if I hadn't use anything but I don't really think it actually stops anything. A lot of my friends would say the same. I used Bio Oil afterwards as it is meant to reduce the appearence of the marks already there, I must admit I didn't use it long enough to do anything, but I do hear it has been great for a lot of people.
GL with it all, I do hope you're one of the lucky ones that have no marks at the end of it all!