There must be something in the water! Two of our clients are having twins. Our clients will be training with us right up until the babies decide to show their faces.
The main things to think about if you are pregnant and exercising: keeping your temperature down, keeping your heart rate at the right pace for you.
There are recommended rates but like anything you need to take into consideration your exercise history etc but FYI Australian guidelines state 140bpm and USA 160bpm. Understand that your resting heart rate will be elevated 15 to 20bpm.
This is not a time to make gains, listen to your body.