Pregnancy is not an illness! But it doesn't matter how many times Princess Celestia reminds her servants...
...or the guards...
...or her sister...
they just won't treat her the same. She ruled the country alone for a thousand years for Tartus sake, eleven months of pregnancy is nothing.
It's tagged AU just so people don't moan about any of the issues about pregnancy - if it's not true or matches your view, consider it Alternative Universe. And considering we are talking about magical talking ponies, that sounds fair to me!
Just a short story of a couple of chapters...