I would be so tempted to write back something like,
"Congratulations! I thought for a minute you might be trying to prank us, but then I realized that no one thinks premature babies are a funny April Fool's joke, so he must be here! Yay! Let me know when you are up for visitors!"
For heaven's sake, people. The boss, who made a tasteless joke, SAID SHE AND THE BABY WERE FINE IN THE INTIAL COMMUNICATION. Of course the next thought would be about triage for work. SINCE SHE AND THE BOSS HAVE A WORKING RELATIONSHIP.
Let's direct our flames to the appropriate recipient: foolish, insensitive boss.
Story time : I had a family member call me and go into detail about how her H was moving to germany for a few months and she was going to be alone and blah blah blah. I listen and invite her to my home if she didn't want to be alone etc.. Then she says - hahaha, I got you!! This was a prank.
WTF prank is that!! That's not even a prank. That's just you calling me and lying. I still get flamed by her family for having no sense of humor but DUDE. Why is this funny!!! It's dumb, yes but not funny. Ugh.
"You. You and your crazy life. You and your geographic anomaly. You and your drunken lesbianic ways and terrible navigational skills." - ProfArt and her holy baby