Bryan and Fola Nelson were excited about their forthcoming five-night Bahamas cruise on the Carnival Fascination. It was to be their last vacation before the birth of their first child.

Then, not long before their scheduled departure, Carnival delivered some bad news: Not only would Fola Nelson be denied boarding, but the cruise line would also pocket her entire fare, minus port taxes.

Why? Because like many other cruise lines, Carnival bans passengers who are 25 weeks or more pregnant.

"My wife will be 10 days over that," said Bryan Nelson, a teacher in Minneapolis. "And despite her doctor's OK, the cruise line is sticking to its policy."

Cruise lines' rules on pregnancy are a common source of complaints from travelers. But like so many other cruise industry policies, this one wasn't always a hard-and-fast rule. Had Nelson become pregnant a decade ago, the company probably would have let her reschedule her trip at a minimal cost.

Not today. And the change is something the cruise line seems happy to let the world know about.

Carnival's policy allows pregnant women to sail only through the 24th week of pregnancy. Every passenger who is expecting must show a physician's letter verifying that mother and baby are in good health and fit to travel. The letter must also include the estimated delivery date. "Carnival's pregnancy guidelines are put in place as a precaution to protect the unborn baby and the mother," said Aly Bello, a spokeswoman for the cruise line.

That makes sense. Cruise ships have reasonable emergency medical facilities for guests and crew. But prenatal and early-infant care can require specialized diagnostic facilities or treatment that might not be available on a ship or in the closest port of call.

Even with such rules, complications can arise. In November, a 31-year-old passenger was airlifted from the Disney Magic, 180 miles off the Texas coast, because of medical problems related to her pregnancy.

Other companies have virtually identical policies. Norwegian Cruise Lines refuses to admit passengers past the 24-week mark. So does Royal Caribbean Cruise Lines. "This decision is made because of the unique nature of a cruise ship being at sea for extended periods of time and the possibility of a guest's medical condition becoming critical during those times at sea," Royal Caribbean spokeswoman Cynthia Martinez said.

But not every pregnancy is planned, and cruises are often booked months in advance. You'd expect cruise lines to help passengers who get pregnant in the months between booking and sailing dates, particularly if the company can resell the cabin.

But Carnival turned down requests from the Nelsons and their travel agent to waive its rules. Bello noted that the Nelsons should have bought the travel insurance Carnival offered. If they had, they would have received a 75 percent credit toward a future cruise.

That's becoming an increasingly common response. Cruise lines appear eager to make a public example of customers who didn't buy travel insurance. The reason? Travel protection now accounts for a significant share of their profits, and bending a rule would effectively undermine the business model.

"I don't think it's unreasonable for the cruise lines to adopt pregnancy policies, particularly given the limited nature of the medical facilities on cruise ships and the absence of doctors who are experienced in obstetrics and gynecology," said James Walker, a Fort Lauderdale, Fla., lawyer specializing in maritime law. "The problem arises when there is a good-faith misunderstanding by the pregnant passenger, and the cruise line takes a rigid attitude and pockets the consumer's money."

The Nelsons say they're troubled by the way their situation was handled. Neither their travel agency nor Carnival disclosed the pregnancy restrictions clearly before they booked, they said. "We reviewed cruise tickets from our travel agency and found nothing about pregnancy," Bryan Nelson said.

I asked that agency, Cruise Vacation Outlet in Orlando, what it tells customers. Todd Elliott, the president, said the agency directs all clients to complete an online check in to review terms and conditions. The agency's welcome letter to new customers also directs them to the terms and conditions, which contain information about cruise lines' pregnancy restrictions.

In an e-mail to the Nelsons, their travel agent, Jay Garcia, put it on the bottom line: "We are not responsible for unforeseen circumstances that are beyond our control."

Nelson wasn't satisfied with that response. He said that the welcome letter refers only to visa and passport requirements and that he was never told to review the terms and conditions on the cruise line's website. His wife's pregnancy was flagged a few weeks before the cruise, when they tried to check in online.

Even if they'd booked their cruise using Carnival's website, they would have had to wade through four screens of information before reaching the details about pregnancy. It's easily missed.

As someone who once had to postpone a family cruise because of the 24-week rule, I'm sympathetic to Nelson's problem. I don't think it's right for him to lose his entire cruise. No one is arguing that the cruise line policy is wrong. But waiving a rule for a borderline case such as the Nelsons' wouldn't affect Carnival's stock price, and it would go a long way toward creating loyal repeat customers.

At any rate, making an example of the Nelsons seems insensitive and opportunistic - even if the cruise line's contract allows it.

Christopher Elliott's Travel Troubleshooter column appears on N2.

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