I would lift things at work I was a waitress, and lift my son 3yrs old because I always did I ended up getting an anatomical hernia and it hurt s like hell. Not worth it.
Be sure not to put your hands over your head with the lifting.. I've heard the abilical cord can wrap around the baby.
I was very fit before pregnancy, did insanity for 2 yrs and could run 7 miles. I continued to lift and pull at work *nurse* and started to bleed at 29 weeks. .... they say I had a small abruption possibly due to lifting. I haven't lifted since, not worth it.
Short answer, there is always that chance you could injure the baby especially the further along you are. With that being said, if it something you're used to doing than you should be okay but be more careful the further along you get.