There are a lot of pg women at my gym who have continued their workouts right up until they were due... (and they are such an inspiration!)
Most pg women I know there have had to slow down their pace a little bit though after about the 20week mark... This is probably a good thing, because your heart has to beat harder/more blood when you are pg, so it becomes easier to overexert yourself as your baby is growing bigger inside you.

3 main things to be careful with are:
Weights - because pg hormones relax your ligaments making you more prone to injuring or pulling something.
Also stomach excercises, such as crunches etc... just check with your gym instructor as to what stage of pregnancy you should stop doing them. I have heard you need to stop the stomach excercises pretty early on in pg.
Also be careful not to overheat too much...

Because you have been excercising for so long though, I really wouldnt be too worried, and would just follow your own body cues.

Goodluck!