It is important that you consult a health care provider or visit a travel health clinic to discuss your travel plans, preferably six weeks before you travel. The safest time to travel is between the 18th and 24th weeks of pregnancy. Most common obstetric emergencies occur in the first and third trimesters.
https://travel.gc.ca/travelling/health-safety/travelling-pregnant
1 This prevents blood clots from forming in the legs and pelvis.  Keep your travel plans as flexible as possible. Problems might develop at the last minute and you might have to cancel your trip. Unless it is absolutely necessary, do not plan any trips during the third trimester of your pregnancy.
http://www.babymed.com/pregnancy-safety/travel-and-pregnancy
If you plan to travel, discuss the trip with your health care provider. Generally, the safest time to travel during pregnancy is the second trimester (13 to 28 weeks). At this time you probably feel your best and you are in the least danger of having a miscarriage or premature labor.
http://www.babymed.com/pregnancy-safety/travel-and-pregnancy
1 Trains usually have more room to navigate and walk. The restrooms are usually small. It is essential to hold on to rails or seat backs while the train is moving.  Try to limit the amount of time you are cooped up in the car, bus, or train. Keep travel time around five to six hours.
http://americanpregnancy.org/pregnancy-health/traveling-during-pregnancy/
Traveling by Air During Pregnancy. Whether you are going by car, bus, or train, it is generally safe to travel while you are pregnant; however, there are some things to consider that could make your trip safer and more comfortable. It is essential to buckle-up every time you ride in a car.
http://americanpregnancy.org/pregnancy-health/traveling-during-pregnancy/
1 Pregnant travellers can normally travel safely by air. In the absence of medical or obstetrical complications, pregnant women can safely fly up to 36 weeks gestation.  Most airlines restrict travel in late pregnancy or may require a written confirmation from a physician.
https://travel.gc.ca/travelling/health-safety/travelling-pregnant
Timing of travel. 1  The safest time to travel is between the 18th and 24th weeks of pregnancy. 2  The decision to travel should be made in consultation with your health care provider.  If you decide to travel while pregnant, make sure that you have proper travel health insurance.
https://travel.gc.ca/travelling/health-safety/travelling-pregnant
1 The safest time to travel is between the 18th and 24th weeks of pregnancy. Most common obstetric emergencies occur in the first and third trimesters.  The decision to travel should be made in consultation with your health care provider.
https://travel.gc.ca/travelling/health-safety/travelling-pregnant
1 The gas used in air bags is won't hurt you or the baby. If you are in an accident, you should see a doctor to check you and make sure you and your baby are fine. 2  Adjust your seat as far from the dashboard or steering wheel as possible.  Motorcycle travel is not recommended during pregnancy.
http://www.babymed.com/pregnancy-safety/travel-and-pregnancy
1 Try to limit the amount of time you are cooped up in the car, bus, or train. Keep travel time around five to six hours.  Use rest stops to take short walks and to do stretches to keep the blood circulating.
http://americanpregnancy.org/pregnancy-health/traveling-during-pregnancy/
at how many weeks in pregnancy should you not travel
You should not travel in the first and third trimesters of pregnancy.  you should not travel In the first and third trimesters in pregnancy .