If you are low risk and no medical conditions, typically docs will say to only do what you were doing before and no more. So now wouldn't be a good time to take up running but if you were already running frequently there shouldn't be a problem. Treadmills do get frowned upon later as your balance becomes iffy and its more likely to have a fall.
When in doubt- ask your doc!
April 2014 May Siggy Challenge: Funny Animals- Kangaroo Mating Ritual
Re: What pace to walk 1st trimester?