I'm 37 weeks and have none so far. I know I'm prone to them as I got them on my hips at puberty. From early in pregnancy I've been super careful with my diet. I drink loads of water and eat foods that help boost skin collagen production - anything with vitamin E, oranges, good fats such as avocado and soya lecithin (I sprinkle this on my cereal). Avoid foods that dehydrate - caffeine, processed foods, salty snacks etc. Use a good natural vegetable based oil or or cream every day after you shower. Put it on everywhere as the skin is one organ, so even though it's just your belly and boobs growing you could get stretch marks on your things or bum. I personally make my own oil by melting bees wax, coconut oil, olive oil, rose hip oil and adding in essentials oils frankincense, lavender and myrrh and some vitamin E. I think I got the recipe on Pinterest btw. It has worked well so far! Good luck!
Keep a healthy diet during ur pregnancy so u don't get too big to fast. Since rapid weight gain causes tears underneath ur skin which is what causes stretch marks but also say very hydrated. So u skin can stretch. And generic plays a huge role on getting stretch marks. But coco butter and lotions help with the dryness so ur skin is hydrated. And to lose ur belly fat well if u don't over do it with a high fat diet during pregnancy it shouldn't be to hard. A flat stomach is mostly diet and cardio but more importantly is ur diet. After My last pregnancy I had a completely flat stomach in 8 weeks but I exercised throughout my pregnancy and a week after deliver I started a low fat high protien diet and lots of cardio and weight training. Was showing my belly in no time. I plan to do the same after this one.