Did your mom get stretch marks? Does your sister have 'em? Your cousin? If so, you're more likely to develop them yourself.
A possible genetic component is just one of the risk factors for stretch marks, but it's one that's beyond a woman's control. Large baby size, carrying twins or triplets and excess amniotic fluid are other factors that fall into that category. Some of the others factors, though, are more open to outside control.
How much and how quickly a pregnant woman gains weight, for instance, affects her chances of developing stretch marks and, if they show up, how severe they are. A 50-pound (22-kilogram) gain is going to cause the skin to stretch more than a 25-pound (11-kilogram) gain, and a 25-pound gain over three trimesters will give the skin more time to adjust than the same gain in the final month.
Another controllable risk factor is diet. A healthy one can decrease the severity of stretch marks. In particular, consuming lots of water along with a nutritious intake of silica, vitamins A, C and E, healthy protein, and zinc can increase skin's elasticity, while over-consumption of caffeine can decrease it [source: MedicineNet].
As far as spending money on stretch-mark prevention, you're not going to get that much of a return. Lots of people swear by over-the-counter creams, lotions and oils, but there's really no reliable evidence they work to prevent anything except itchiness -- which is no small feat [source: BabyCenter]. Skin irritation often strikes pregnant bellies as a side effect of the stretching and the hormones. Applying ingredients like lanolin and cocoa butter may not do much in the stretch-mark realm, but they can do wonders for other skin issues, so apply away.
If you're looking for positive side effects, all of these prevention methods are good prenatal choices. Lotions soothe the skin. Complete prenatal nutrition helps keep mom and baby healthy. Slow, moderate weight gain is easier on the body than the fast and extreme kind. Unfortunately, they may not prevent stretch marks. If your skin isn't elastic enough, you'll probably end up with some streaks.
That's when the post-natal action comes into play.