They say that if your body is used to working out to that extent then it is fine but if you're just now going to start it could be harmful, definitely talk to your doctor.
My doctor had told me that I could continue exercise/running as before I got pregnant just not to over work myself Nd if I get tired or don't feel good for me to slow it down . as long as you don't over work your body you should be fine. But just to make sure still ask your doctor.