I agree with what most of the ladies have said - it really depends on what physical condition you were in before you got pregnant.

Like Natty, I am also a competitive runner and triathlete - I agree that it is not so much that your heart rate should be under a certain number, but like Natty has said, you don't what to run/excerise so hard that you are gasping for breath.

The hardest I will run is when it feels 'comfortably hard'. I know this is a hard concept to explain, but easy if you are a regular runner. It means I can run but still speak in short sentences.... and I am not feeling over tired. Mostly however, runs are done at a more comfortable pace, and swimming and stationary cycling NEVER seem to elevate my heart rate as much because they are NON impact I suppose.

I ran 6 days a week for 9 months with my first....no problems. This pregnancy, I am 15 weeks and feeling not so fit, I am older (of course!!) but still managing 5 times a week and swimming 3 times a week.

Keep cool (exercise is MUCH better OUTSIDE in the cool mornings!). Rest when you are tired........ and don't worry too much.