It recently happened to Samantha Cameron, wife of British Prime Minister David Cameron, who was on holiday with her family in Cornwall when she gave birth on Aug. 24 to a daughter – a baby who had not been expected to arrive until September.

The cesarean delivery was at Royal Cornwall Hospital, and everything turned out well for mother and daughter Florence.

Michele Hakakha, co-author of Expecting 411, a new guide to pregnancy and childbirth, says travel advice for pregnant women varies depending on the mode of transportation and how far along they are.

“The one concern that is across the board for all trimesters and all pregnant women is sitting for long periods of time, whether that's on a plane or a boat or in a car, and that's the increased risk of developing a blood clot,” Dr. Hakakha, an obstetrician-gynecologist in Beverly Hills, Calif., said in an interview. (The other co-author is pediatrician Ari Brown.)

She recommended that pregnant women get up and walk around periodically, and wear support stockings to help improve circulation. “Typically if you’re pregnant, you have to go to the bathroom all the time anyway, so it's usually not an issue,” she said. “You have to pull over your car, or you have to get up from your airplane seat and move around.”

Pregnant women who flip through travel brochures pondering a cruise or flight need to ask questions about medical care and restrictions.

Most cruise lines will not allow women to travel in their third trimester, Dr. Hakakha noted.

“Airlines will let pregnant women fly up to 36 weeks, which is four weeks before delivery. However, individual ob-gyns may have different cutoffs. I typically let my patients fly up to about 32 weeks,” she said, adding that women should check with their own practitioners.

A woman with a normal pregnancy and no previous history of premature labour can travel up to and including the 36th week at Air Canada. Airline spokesman Peter Fitzpatrick said any queries can be put to the airline’s medical desk.

Dr. Hakakha said there should be no travel on small planes or small boats after the second trimester.

“If something happens and you're on a remote island or you're in the middle of the ocean or you're on a tiny plane where there’s not going to be anyone to help you, it’s a really tough situation,” she said.

“Trains and cars are fine. Usually in your third trimester, you want to stay pretty close to home, and that means that if you want to be within an hour or even an hour and a half, that’s probably fine.”

Otherwise, if the pregnant woman starts bleeding heavily or her water breaks, she will need to go to the closest medical facility – without her prenatal records or a familiar doctor on the case.

Almost daily, Dr. Hakakha said, she gets asked about airport scanners.

The older airport scanners are really just “glorified metal detectors” and they’re completely safe, she said, and the new full body scanners being introduced are also fine.

“They've actually estimated that you’d have to go through 2,500 times during a pregnancy to actually potentially cause some damage.”

Food is always an issue for pregnant women, who need regular sustenance. Dr. Hakakha advised having healthy foods on hand, such as almonds, apples, carrots or peanut butter.

“It’s better to do eight small meals than three big ones. But keeping snacks with you at all times is really important so you can avoid those long periods of time where maybe your plane is delayed or your husband took the wrong street and you're driving for a lot longer than anticipated.”

Those travelling to foreign destinations, such as Europe, need to be aware that a lot of places have unpasteurized dairy products, which could contain listeria, or raw meat or fish that could cause the infection toxoplasmosis, which can be dangerous for pregnant women, Dr. Hakakha noted.

“Your immune system is completely suppressed when you’re pregnant,” she explained.

“It’s the only time in your life you’re carrying foreign DNA in your body and you’re not rejecting it. and so in order for your body to do that, your immune system is suppressed and you are much more likely to develop food poisoning or contract things compared to people with you in the group that are eating the same thing.”

Ensure that raw vegetables are washed thoroughly. Alternatively, she advised sticking to steamed or cooked vegetables.

Pregnant women need to stay hydrated but should stay away from drinking bottles made of the hard plastic that contains bisphenol A, which could be dangerous for fetuses, she said.

If a woman who is expecting does become ill while travelling, and is vomiting, has diarrhea and fever, she should contact her doctor at home to discuss whether she should head home.

“But certainly, if you get sick, there’s no harm in going to a local hospital or an urgent-care centre to be seen.”

In terms of a travel kit, Dr. Hakakha said women should take along acetaminophen for headaches and an anti-diarrhea medication – just in case. Bug spray is safe and recommended, she said, because “the last thing you want to be when you’re pregnant is itchy, because you’re already hot, you weigh more than you normally do.”

Pregnant women should stay away from Jacuzzis, hot tubs and saunas because elevated body temperatures in the first trimester could lead to neural tube defects in fetuses, or dehydration or fainting of the woman in the second and third trimesters, she noted.

People providing spa services need to be informed of the pregnancy, even if it’s early days, because it will alter what they can and can’t do.

“It’s important because if you're having a facial, for example, certain products may not be okay on your skin, and your skin may be a lot more sensitive,” Dr. Hakakha said.

“And if you're having a massage, no matter how far along you are, there are certain trigger points that should be avoided that can potentially trigger ... contractions.”