The best advice here would be to pay attention to how you feel, and if you’re in any doubt, contact your doctor. Some women can exercise with no trouble until their third trimester, while others need to take it easier.
A good rule of thumb would be to take regular classes if you prefer them to prenatal ones, but to avoid any contact sports or classes, like karate or judo. High impact aerobics classes and running might also be difficult to manage, but again, your body will be your best guide.
It’s important to remember, notwithstanding any of this, that your doctor knows best. If he or she recommends that you stop exercising, or even that you stay off your feet for a while, you’d be well advised to listen. After all, the safety of your baby and your own health is more important. You can work off the baby weight after your child has arrived, and your life has returned to normal – or at least as normal as it will be with a baby around!