When should i tell my boss if i am pregnant?

After 12 weeks: Unfortunately, most miscarriages (if they occur-hopefully not!) take place within the first 12 weeks of pregnancy. To be on the safe side statistically-speaking, one should wait until after 12 weeks in general to let anyone know including your employer. We live in the world of twitter and facebook so be conscientious before sharing the good news...Just in case. I hope this helps.

This is completely: Up to you. Most like to wait until after the first trimester, when miscarriage is less likely.