This story asks the question and mostly answers with a resounding guess so. Allow me to be more blunt. Hell yeah, you should.
Now obviously you should check with your doctor, just in case. Some pregnancies are more complex or fragile than others. But assuming yours is healthy and not unduly complicated, knock your socks off. I trained through three pregnancies and was back in the dojo within days of giving birth to each baby. I have also helped other women exercise while pregnant. It's not only feasible, it's excellent.
One, because it will help you not gain too much weight. Two, because it's good to keep up healthy habits. Three, because working out helps you deal with those stupid hormones. Four, because it feels good. Five, because it will also help you sleep better (see "stupid hormones" above).
A few things though: A pregnancy is not the best time to start something intensive and new. If you've never done karate before, wait until after baby is here. Focus instead of doing something your body already knows how to do. Also, speaking of your body: Listen to it. If something doesn't feel right, don't do it. I modified a bunch of exercises to accommodate my growing belly, sore back and what have you. The point isn't to keep doing splendid burpees. The point is to feel good by exercising as much as is possible under the circumstances. Oh yes, and do try not to push yourself to the point of exhaustion. Lactic acid isn't great for the little one.
So yeah. Go ahead. Exercise. You'll thank me later.