Sorry your MIL is so insensitive, especially is she knows you have fertility issues. I think you should tell her to shove it.
Can your DH say anything to her to get her to lay off and quit saying rude things? Otherwise I'm sure we can help you come up with a whole list of snarky comebacks, like, 'Yep, looks like you'll be scooping poop instead of changing diapers.'
My MIL has just started saying
if we have kids rather than
when, anymore. It feels a little like she's given up on us, but at least it's not mean spirited.
Good luck and I hope she lays off soon.
I used to visit this site quite a bit when I was first married:
Mother-In-Law Stories and Mother-In-Law Jokes
There's this one too:
Granny Dearest Stories | Mother-in-law Hell