if you are doing it already, it should be ok but do listen to your body. My trainer told me I wouldn't have to change a thing until I got to 2nd trimester and I train relatively hard. Most sessions, I get my HR to 90% of my maximum and when pregnant I was reaching 80% (approx HR of 165). My GP also told me the same thing. That I didn't need to change a thing.

Having said that, if you don't feel comfortable doing it, then don't.