My pregnant friend and I rented a hotel but I'm thinking of cancelling the reservation without telling her first.
What would make you want to cancel your plans before consulting your friend?
Their pregnancy comes with so many issues and I can't deal with that right now.
You should have a good reason to cancel a reservation last-minute, because otherwise, that's just rude and inconsiderate. If you must cancel, try to make it up to the person at a later date.
But I can't enjoy my vacation when I have to deal with an emotional wreck of a friend. She should realize what a burden her pregnancy is.
It doesn't matter your reason, really. You can cancel a reservation if you want to, but you shouldn't have done it without consulting her first. You're going to hurt her feelings.