I think there's a lot of conflicting data on whether using coco butter or bio-oil actually helps.
I think the majority opinion is that for the most part whether you get stretch marks or not depends on whether your mother had them when she got pregnant (so, there's a genetic component). Coco butter does help with skin hydration and prevents the itchiness associated with stretching skin. Stretch marks are caused by the elastin breaking down in the dermis due to rapid weight gain or constant stretching of the skin (both found in pregnancy). Some people think that it may help a little because massaging lotion or oil in the skin causes an increase in circulation which helps prevent elastin breakdown.
I think it just comes down to if you're going to get them (due to genetics), there's nothing you can do to stop them....but using coco butter won't hurt and
may help a little.
My mother got a lot of stretch marks
. I'm still going to be slathering on coco butter every day though! Just in case