I flew to the UK from perth which was 19hrs all up when I was 4 months pregnant and I was fine, I did ask for a seat with no seats in front so i could stretch my legs but they gave me one at the back so i could lie my seat back.. they were great..and the stewardesses were always coming and asking if i needed a drink or anything to eat..

i know what u mean about being worried, I was worried when i flew and it was my first time flying aswell.. but it all turned out ok, maybe ask your GP for some advice aswell?

take care
Lesley