2nd pregnancy, no new stretch marks?

Rebecca
First pregnancy: stretch marks galore, even down below! There seemed to be no end to it. Now in my second pregnancy I've made it past 27 weeks and nothing! I'm not carrying any smaller. Of course I have the scars from my old stretch marks, but no new ones. 
This happen to anyone else? I thought stretch marks were mainly genetic, but now I'm wondering if they are hormonal as well.