Having worked with models who gain 50 lbs with their pregnancies and 3 months later are back to doing bathing suit shoots, I had a few tricks up my sleeve to avoid stretch marks during my pregnancy. Their advice worked, and so I pass on their wisdom to you:
1. Get in your best shape ever before you get pregnant so that your skin can accommodate the weight gain. Also, if you're at a healthy weight you'll have more chance of conceiving.
2. Don't gain more than the recommended 25-35 pounds, not good for you or baby. I gained 30 and it was a cinch to lose and I didn't diet (another reason breastfeeding is fabulous).
3. Drink lots of water, eat lots of fruits and veggies to stay hydrated.
4. Eat lots of good fats, very important for skin's elasticity.
5. Keep moving, long walks are great.
6. 'You must put oil! Start now! We only have one skin!' This is according to my Brazilian-model friend who has 3 children and looks disgustingly fabulous. I had just found out I was pregnant, so nowhere near beginning to show in the tummy, but apparently that's the time to start caring for the skin. The oil she recommended was sweet almond oil (easily found in pharmacies) and I applied it at least 5 times a day to my belly, hips, boobs, and thighs, as per her instructions.
7. A couple of other products that were recommended to me that I liked were Clarins Tonic Oil (a product French women swear by) and Mustela 9 Months Stretch Mark Cream. I didn't use them as often as the sweet almond oil though, I preferred to use something more natural since I was applying so often.
And there you have it. Though I must mention that even if I did get a belly full of stretch marks, gain 100 pounds, ruin my vagina, or any other things a first-time Mom worries about, it would still have truly been worth it. Of course you don't realize that until after your baby is born. When it's your first pregnancy life's still all about you and your worries about yourself, and when baby comes along things change so drastically. Enjoy your solitude, the anticipation, and take good care of yourself. Enjoy your pregnancy.