My kids are bigger than me now, 15 and 20, but I lifted at the gym using heavy weights for both. However.......your doctor is the first person you should go to with this. Rule of thumb, if your pregnancy is free of problems, you usually can do what you did before, with modifications as you grow. Also other considerations are you will have increased fluids, may feel ill things like that.
With kid number one, I worked out both cardio and weights until 8 months. At that point I had preeclempsia, most likely from work stress and was put on bed rest. With kid number two, I did weight lifting up until a week before I had her. Using the squat rack got me some wierd looks. I stopped when my hips started getting funky feeling....she had dropped.
Believe me, being fit helps with delivery and recovery!