After reading a few recent posts on here about how to word FB postings, and remembering the sting of all the posts during our years of TTC, this is what I came up with. (Thanks to those whose words I stole or paraphrased - I can't give you exact credit because I borrowed from so many!)
"After three years of wishing and hoping, we can happily share the news that we are expecting a baby in March! Today marks the halfway point, and we had a healthy baby scan this morning. Keeping our fingers crossed that everything continues to go well. To those of you out there doing your own silent wishing and hoping, I hope you get your own good news soon too."