So, I'm a slacker... or that's what I felt like at my last prenatal appointment. I was relating my symptoms and mentioned I get very out of breath going up stairs, etc. when my midwife told me that I needed to get off my backside and get my heart rate up. Or at least it was something like that...
30-40 minutes of cardio at least 4 days a week. Which is about 3 days more a week than I was exercising at the time.
I'm up to 4 days a week (usually) of either brisk walking on my treadmill, or a prenatal pilates workout, or a little of both. I've found that I don't get quite as out of breath on the stairs, but I do still "huff and puff".