I know people will tell you its genetic/hereditary and nothing can be done about, and if your mum got them you will too.
I don't believe it at all, and here's why.
My mum has a ton of stretch marks on her belly. she never used any creams on her belly during any of her pregnancies.
My youngest sister is the same. never used any creams on her belly either, ate unhealthy as well, and has a ton of stretch marks from her first and then her second pregnancy.
then there is my other sister.
Applied moistureiser to her belly every day from when she first found out she was preg, ate pretty healthy, and drank lots of water, and did nNOT get one stretch mark. So you can't tell me she was just "lucky". NO if that theory holds any water, then regardless she should have gotten stretch marks too.
I am in my last trimester and have no stretch marks so far, which I am glad of. Yes, I applied creams as soon as I found out I was pregnant, have drunk lots of water, and eat pretty healthy, occasionally not so of course.
So dont let anyone tell you that you cannot avoid or prevent them! ;-)
I do think also that only putting on the recom mended amount of weight during pregnancy is a good thing. Don't put on excess weight as that will put more stress and strain on your skin.