Honestly, you can just maintain your weight as best as you're able and you'll be fine. People don't actually need to gain the 10-15 pounds recommended for overweight women, and that's even more true for obese women. My doc advised me to just eat as best as I was able to, exercise without wearing myself out, and try to maintain. He said it would be fine if through doing this, I lost too. And initially I did, I started at 235, through the first 20 weeks, went down to 226 and then back up, and then ultimately gained 8 pounds by 39 weeks, 12 pounds by 40 weeks. (I seriously believe that last week was all water retention since I didn't start swelling until then!)
Anyways, if you maintain, you'll have such an easy time whoosing your way into the 100's after the baby is born. Plus if you're doing it by eating healthier and truly listening to your body, baby will be getting everything it needs as well without starving yourself!