Most all of the other cruise lines require that the infant be at least 6 months old at the time of sailing for most sailings, and a year for certain sailings.
Expectant mothers must be 23 weeks or less at the time of embarkation which is 6 months and will need to provide a doctor’s note certifying good health.
The only exceptions to that 6-month infant rule is MSC!
Infants can travel at any age on MSC cruises!