Travel by any means, automobile, bus, train or plane is fine in pregnancy. The most important thing to remember on longer trips is you need to get up and walk each hour. If you do not, you increase your risk of developing a blood clot in your legs due to poor circulation. Support hose are also recommended.
You may travel at any time during your pregnancy, there is no cutoff date. Obviously the closer you get to your due date the more likely you are to deliver your baby somewhere other than Frisco, Texas. Common sense tells you, if you are already having pregnancy complications and you decide to travel, than you risk being taken care of by an emergency room physician, in another state or country, who is unfamiliar with your medical history.