Working and pregnancy

I have many women brag and say "oh I worked right up until the day I popped!" Which I'm sure is true and good for you but did you set restrictions for yourself in the workplace?I'm worried that setting restrictions for myself, especially since I'm starting new employment, may be frowned upon and my coworkers may get the lazy first impression of me.  I've worked with many women who have milked pregnancy to get out of job duties and I don't want to be that woman. As a coworker what would you consider a reasonable ( not ordered by a doctor) restriction? For example I work in a psychiatric hospital. As a cautious soon to be mother, I ideally would opt out of physical altercations with patients or transferring immobile patients to other surfaces. (Aka trying not to get hit in the ever so vulnerable stomach and avoiding lifting 50+ pounds).  How understanding should coworkers be?