The Jurlique oils are great, especially Almond Oil. You have to start using it the minute you find out you are pregnant and carry on using it twice a day - morning and night! It's a good habit to pick up anyways, because our skin gets thirsty right, and if you are thinking of having more kids, it only gets worst if you don't look after yourself now?
However, I don't believe it's genetic, I had stretch marks on my tummy and they've now disappeared. You just have to be very diligent and massage the creams/oils into your skin (your skin is made up of 7 separate layers, so imagine trying to get through all that?), don't be sloppy about it! Another great brand I use for my bum is Murad's toning cream. There are two tubes you have to apply, one after another, and I bought it from Elle Spa in Repulse Bay. It's worked wonders and I've only been using it for 2 months!
Trust me...the costs are worth it!