We are in exactly the same situation. We have a 20 month old with CF and went through very similar discussions about what the second one might feel having a "sick" sibling, being the "spare" to the "heir", and the great measures we went through to prevent a 2nd with CF. We have since concluded after a year of talks, that both children may have issues and baggage and questions and troubles, but the heart of it is they will also have each other. My husband and I value our siblings so much ESPECIALLY while going through all this drama with CF. We want our daughter to have as "normal" a life as she can. And to us that means siblings. She deserves it and so do we. This stupid disease has taken enough from us, you know? We are starting IVF in summer. Good luck with your choice.