Exercise during pregnancy?

[confused]

I'm the type of person that always exercises even before I got pregnant. I'm now six months pregnant with my 1st... With my dr's permission I've been doing prenatal aerobics 3 to 4 days a week. I plan to keep exercising all the way, with the arobics or walking. My question is how much will this exercise help me during labor and after the baby. Please let me know from your experience if you exercised all during your pregnancy what difference did it make? Thanks