Running While Pregnant

I found out I was pregnant not even a week ago and I've been training for a marathon (will not be running the marathon anymore). My average weekly mileage is 30 miles with the longest run being 15 miles. I've heard that it is safe to continue running what you already have been but I feel like I can add more mileage to my long runs (16-18 miles). Does anyone have experience with this? I'll ask the doctor when I see her late next week.