Announcing your pregnant to your kids

Amanda • Mommy of 2 beautiful girls!
So hubby & I found out we are expecting number 2!  We are only 4w along. I want to tell our daughter but I'm afraid Bc it's to early and if case anything happens how do I explain that!  Our daughter is 5 and extremely smart. She wants nothing more then to be a big sister. So do I tell her or wait 2 weeks till my next doctor appointment??  What did you ladies do?