Hi there, this is from our disney e-ticket contract from last year.
Pregnancy/Infants
Women who have entered their 24th week of pregnancy as of their embarkation date will be refused passage due to safety concerns. Neither a physician's medical statement nor a waiver of liability will be accepted. In addition, Disney Cruise LineĀ® cannot be held responsible or liable for any complications relating to pregnancy at any stage. Infants under 12 weeks old will not be allowed to travel aboard Disney Cruise LineĀ® ships.
Carnival's policy is the same. Hope this helps.