In general, the answer is yes. Under normal circumstances, travel during pregnancy is safe until the last 5 weeks or so of pregnancy. This includes flying. Most cruise ships will not allow you onboard if you are pregnant past a certain gestational age. Be sure to drink plenty of fluids, walk, and stretch your legs on long trips.
You should take normal precautions while traveling, such as wearing seat belts. The lap belt should be below your belly so that it fits snugly across your hips and pelvic bone; the shoulder belt should be across your chest (between your breasts) and over the mid-portion of your collarbone (away from your neck). Never place the shoulder belt under your arm or behind your back; also, ensure there is no slack in the belt and that your airbags are turned to “on.” Keep 10 inches between the steering wheel and your breastbone. You may need to angle the steering wheel toward your breasts, not your belly or head.
There is nothing inherently dangerous about traveling by ground, sea, or plane during pregnancy. However, you do have to consider how long you will be separated from the ability to seek medical care, and how far away that medical care might be. This is more important in the third trimester, particularly in the late third trimester when labor is more likely. It’s for this reason that many cruise ships will not allow you to embark after 24 weeks’ gestation. They do not want any liability related to premature delivery when the baby has a chance to survive preterm. It’s not that sailing isn’t safe, it’s only that it is many hours away from a hospital.
Planes do not often limit travel by gestational age, but you should consider how long your flight is. There is a big difference between flying from Atlanta to New York versus flying from New York to Melbourne. In general, many doctors recommend avoiding flying after 35 weeks’ if the length of the flight is particularly long. Some people worry about traveling by car due to the concern of increased risk of blood clots secondary to the immobilization of sitting in a car. This is probably not a valid reason to avoid travel by car, particularly when you consider that pregnant women will be taking pit stops every two or three hours anyway. When you stop for a potty break, be sure to walk around for a couple of minutes.