We lived in UK. My wife had pregnant when the baby was about 3 mths. We travelled from UK to HK (12 hrs direct flight). Then we flew back from HK to UK after 1 month stayed in HK (we even went to Thailand during that time). The doctor here said no problem anytime between after first and last 3 mths. ie 3 - 6 mths ok.
Of couse, I would suggest you to consult your doctor.