I traveled internationally (14+ hours each way) this summer while pregnant. I left when I was 13 weeks and returned when I was around 30 weeks. I also did another short (3 hours each way) international trip (left at 32 weeks and returned at 34 weeks). I have also traveled internationally with my first two pregnancies (my children are now 8&5).
You are safe to travel by plane from the beginning of your pregnancy all the way up until the end portion of your last trimester (usually 9th month - 36 weeks) and can manage what ever kind of trip(s) you want to do as long as you and your pregnancy are healthy and the pregnancy is progressing normally. As long as everything is fine, air travel does NOT increase the risk of miscarriage or pre-term labor.
You need to get a check-up from your doctor to make sure that you are in fit enough health, and that the pregnancy is healthy enough to allow for you to fly. Most airlines will require a medical certificate from your doctor dated 24-72 hours before your flight once you reach your third trimester (27 weeks), so you should check on that.
All airlines make up their own rules and regulations regarding pregnant women. Some do not restrict travel at all, no matter what stage of pregnancy a women is in, and others start to restrict at 7 months, although the majority restrict around 36 weeks.
FAA Airline regulations state :
Obstetrical patients are free to fly, but pose a significant risk in later stages of precipitating delivery during flight. Pregnancy past 32 weeks should be carefully considered for restriction from flight and must be accompanied with an authorization note from a doctor. Those past 36 weeks should be prohibited from flying unless personally accompanied by their doctor. (Taken from my husbands flight security and survival manual & FAA site)
http://www.faa.gov/other_visit/aviation_…
While traveling I advise you to keep your medical records, and the name and number of your doctor. You should also get the name and number of a doctor where you will be staying/visiting in case an emergency comes up.
To keep yourself safe and comfortable on the trip, follow these simple things:
*drink plenty of water
*avoid caffeine
*don't eat food that causes gas for at least one day before you travel (pressure builds up as you ascend through the altitudes and could cause pain)
*walk around as much as you can (up and down the aisles)
*stretch while sitting
*wear loose fitting clothing
*wear slip on shoes (your feet may swell)
*wear maternity support pantyhose or socks
*try to get an aisle seat or a front row seat for more leg room
*eat light foods
*eat small meals or snacks at frequent intervals rather than big heavy meals
*do not eat salt
*Wear your seat belt just under your abdomen (depending on how big you are, you can also ask for a seat belt extender - just be sure that that too goes under your abdomen)
*relax
I wrote an article about traveling while pregnant. It gives more in-depth information if you'd like to reference it:
http://jamiehassen79.angelfire.com/pregn…
As for flying after the baby is born, as long as your child has had a check-up with the doctor and everything is fine, your child will be safe to fly almost immediately after birth. Most airlines require that a baby be at least 7 days old, unless you have a medical certificate. I have seen children as young as 1 day old fly. You should call the airline you plan to fly with to see what their policy is. I've been flying internationally and domestically with my children since they were 2 months (now 8&5). At least three trips a year are the children and I traveling internationally (14+ hours each way) alone. In addition to that, we do another 8-10 international and domestic flights a year as a family. I have never had any problems with my children on any of the flights. For information on flying with children (such as security regulations, what to pack, tips and tricks, etc) you can read my article on it here:
http://www.angelfire.com/jamiehassen79/f…
If I can be of any more help or assistance, please feel free to contact me.