I went to Spain (first around 12 hrs from HK to England, then 4 hrs flight from England to Spain...) when I was 8 wks pregnant.
I went to Japan when I was 3 months pregnant.
To me, no big problem as I need to take special care of myself, for example, don't carry heavy luggage; eat healthy food, drink lots of water..........and most importantly, get advice from your doctor and body check before the trip.