Note: An airline can bar you from travel if they are worried about how far along in your pregnancy you are. To avoid delays, and more importantly, to confirm it's safe for you to fly, get written permission to fly from your doctor or midwife. The letter should confirm your due date and state that you have been examined and are not likely to go into labour in the next 72 hours.
Read more here: http://www.babycentre.co.uk/pregnancy/isitsafeto/flyexpert/
Please check your travel insurance policy for any restrictions which apply to travelling whilst pregnant.