I've recently taken cruise on Royal Carribean. They won't accept once you hit 24 weeks pregnancy. I didn't need to bring any gynae letter as I'm less than 23 weeks. You will need to make a health declaration (together with covid stuff) prior to boarding that you're not more than 24 weeks pregnant. Enjoy!
im going in my 23rd week on dream cruises! did get a letter frm gynae that im fit to 'travel' though just in case.
I heard cut off is 24 weeks, not sure if a memo is needed though