It depends, if you've had no problems so far in your pregnancy then it should be ok. It might not be pleasant if you have pregnancy symptoms however.
Information varies and I think you need to decide for yourself. If you have had no bleeding or problems like that, then why not. If you have had any cause for concern I'd discuss with your MW or Doctor first. If you are having a hard time symptom wise you might want to think a while about it. 9 hours is a long haul flight and first tri can and often is exhusting (to the point of feeling ill from it in some cases), so you should also consider how wiped out you may be with commute, flight etc, time difference etc. Then there are the other things, nausea, sickness, food issues, weeing, constipation etc. All can make a 9 hour flight unpleasant. But on the other hand you may feel fine and not notice. Its really impossible to say. If your PG symtoms have not really kicked in yet, you don't know which way you are going to go.
I did some digging and found these
Link 1 At the end they made the following recommendation
“Flying
Where travel is planned during pregnancy, 18-24 weeks in probably the ideal time. Airlines usually allow travel up to the 36th week, but after the 28th week a doctor’s letter may be required stating that the pregnancy is normal, the expected delivery date, and that the doctor is happy for the woman to fly. The policy of individual airlines should be checked.”
The Merck manual on Air Travel (3) states that uncomplicated pregnancy, through 36 week, is not a contraindication to air travel but specifies that high-risk pregnant women must be individually evaluated. They also state that pregnant women should wear seat belts below the abdomen, across the hips and that thrombophlebitis is a specific risk.
Merck also indicate that pregnant women are at higher risk of developing deep vein thrombosis and recommend frequent walks around the cabin and short-movement exercises while seated.
Link 2
Link 3
You also need to ensure you have decent insurance
Good luck
