Congratulations!
Personally, the best way to not gain 80 pounds during your pregnancy is to stay active. Some things, like walking, you can do without changes. Other things, such as strength training, yoga, and Pilates, you need to do with some modifications. (No back lying ab exercises, etc. when you are past your first trimester, etc.)
I would honestly recommend that you exercise regularly. Not only will you have an easier time getting fit after you deliver, but you will have an easier delivery, because you will be stronger physically.
Since the holidays are coming up-why not ask for some prenatal fitness dvds on your holiday list? My favorites were Crunch Yoga Mama, and the Quick Fix Prenatal Workout (strength training). Denise Austin has a brand new prenatal dvd as well.
I tried a lot of them, and the only one I didn't care for was the Kathy Smith one. It is very 80's...and sort of cheesy. ha ha
Just stay active, and watch the junk food. You will be eating more because you are supporting another life...and if you crave a cookie then have it, just stop at 1 or 2 instead of half the bag. Other than that...just enjoy this time.
I Just Found Out...
You must be so excited!! I gained a lot of weight with my first, but with the second I only gained 20lbs. I had gestational diabetes and I worked with a nutritionist throughout the pregnancy. Maybe you could talk to your doctor about referring you to a nutritionist. Keep us posted!
