Normally, if the fetus dies, your body will expel it and you'll have a miscarriage. You'll know when you have a miscarriage because you'll start cramping, your back will hurt pretty bad, and you'll spot like you do when you get your period. IF that happens, you need to get to a doctor IMMEDIATELY... if the sac and the baby are left in too long, it can cause an infection and can even be fatal to YOU.For the most part, 'overworking' yourself [ie. working 50 hurs a week on a salesfloor], shouldn't cause you to miscarry, unless you do suffer from some other complications. When you're tired, tell your boss you need to sit down [given they know you're pregnant]- if they say no, it could mean a huge lawsuit for them. As far as lifting, ask your doctor. Mine said the limit is 20 pounds, but my daughter is 35, so when it became uncomfortable, I stopped holding her so much.