I want to tell my sister I'm pregnant

Geneva
I have 4 children and I am 11 wks with rainbow baby #5. My sisters first born past at a month old then she had my niece who is now 12 and they are trying to have another. They have even been trying vitro fertilization and she has yet to have a success. 
I want to tell her that I am expecting but I don't want to hurt her feelings however I can't keep it a secret long. I only been able to so far because we live in different states. 
What do you all think I should do? How to tell her easily?