I'm 10 weeks pregnant have a bit of an odd job - most days I am desk-bound, but on others, I work on photoshoots, so lots of running around, up and downstairs, carrying things (nothing too heavy), and working from very early until quite late. A 6am-11pm day isn't too unusual (and I can claim the extra time back in lieu).
I feel fine and have had no problems doing this. If I get tired, I rest, and other crew members do the heavy lifting etc.
But… Should I be doing this? Is this overdoing it? It's not going to be harmful to the baby, is it?