How to announce?

Kara

I'm almost 8 weeks pregnant now, and we've announced to my son (from a previous relationship), my mom and SO's mom, step-dad and one of his sisters. We still have 2 of his sisters and both of our dads to tell (his dad lives out of state and will likely be the last to know since SO wants to take a trip and tell him in person)....BUT one of his sisters I'm a little nervous to tell, she's struggled to conceive for some time, and miscarried the one time she did get pregnant, there's possibly an underlying fertility problem and i just don't know how we should tell her without making her feel bad or upsetting her. His mom thinks it'll be okay, and she'll be excited to be an aunt but I don't wanna be the reason she gets down about her struggle, ya know? Any advice or tips??