Dear Rashmi,
Travel by air is safe in the second three months of the
pregnancy (14 weeks to 28 weeks). After that the
uterus goes on becoming more and more irritable and the risk of premature delivery goes on increasing in flight. Though, the aeroplanes have controlled pressure inside, the risk of preterm labour cannot be completely ruled out. So after 28 weeks of pregnancy, air travel, particularly international air travel should be avoided.
The airlines also do not accept the pregnant passengers after 30 weeks of pregnancy without certificate from an Obstetrician; and my experience tells that most of the Obstetricians are reluctant to issue such certificate.
If the delivery process starts on the board, there are constraints of availability of the facilities for conducting delivery on board. Moreover, according to the international rule, the problem of nationality of the baby arises for them. Of course, being Indian, you can opt for the Indian citizenship for you child, however, depending up on the aerial zone of a nation where the delivery takes place, you can opt for the nationality of that country; or the airline itself being a area of the nation to whom it belongs to, you may opt for that nationality also. This is all greatly complicated, hence the airline rules.
I feel you should avoid international travel after 30 weeks of pregnancy. If you are less than that period (7th month), you may choose to travel; however do consider the date of return. If your return is within this time, you may travel.
I hope this provides you a clarity in taking your decision.
Dr. Nishikant Shrotri