I've said this before, and I'll say it again
If your child is past viability (22-23 weeks) or really past 20 weeks when they can start doing medications and treatments to save a mother/pregnancy, I would not travel anywhere where you are not willing to stay for the rest of the pregnancy (and past if the infant needed to be hospitalized.) Prior to 20 weeks, there is very little/nothing that can be done to save a pregnancy btw.
It sounds overdramatic, but while pregnancy complications are rare, when they occur, they are very serious and can threaten the life of the mother and/or the child. If you go into labor and goodness forbid deliver onboard, there will be no one to save your child. There are no medications for a preterm infant onboard and the time it would take to get the baby to a facility, if the child survives, it would likely have severe neurological damage.
The rules are not made to be mean or without good reason or to screw over people who get pregnant unexpectedly. I am a neonatal nurse practitioner and I see people frequently who travel late in pregnancy and end up stranded because their child is born early or with problems and then they are stuck.
Having had pregnancy complications myself, the question I would ask is: is it worth it? If there is a chance it could mean the death of your child, would you want to risk it? Most likely, nothing bad will happen; but if it does, are you willing to accept those consequences? And the guilt?
I kinda view it like I view drunk driving. Most of the time when people drive drunk, nothing happens and they make it home safely. But the times when it doesn't happen that way, are you willing to live with those consequences? I'm not, and because of that, am very anal about alcohol and driving. I couldn't live with myself any other way.
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I just want to add this is NOT only
Disney Cruise Line policy, all major cruise lines have the same policy.
And all of you that have seen pregnant women on-board, I would love you have asked how they were allowed boarding...unless they only seemed pregnant