I just think running with a growing belly will make it easier to fall on treadmill I wouldnt chance it but up 2 u. Also it is not good to overheat so take it easy.
youre aloud to exercise/work out as much as you were before you got pregnant.. and if you wernt and youd like to start id just start with alot of stretching to some little exercises until you reach the level of fitness youd like to do.. for thighs and butt i find swimming to be both fun and very good results in the end
If you were a runner before then you still can, but do not start if you don't do it on a regular basis already. That's pretty much the key when your pregnant you can do most exercises if you were doing them before but do not start anything new. Walking is great, especially on a incline for thighs. I lift weights and do squats/lunges too. Im 22 weeks along
Walking is good also you can take zumba or yoga. No heavy lifting also I wouldnt run.