hi
I worked on a Friday, and my waters broke on the following sunday, and i gave birth on the tuesday.
on that friday i felt like finishing up work, and having a week off to rest - but never got that rest!!
i'd say work for as long as you feel good, and providing your boss will let you take it easy when you need to. i was really active in my preg - gentle gym workouts and swimmimg, so i felt ok to keep working.
hope you enjoy the rest of your pregancy,