There is no reported relations with travel and m/c that I could find. The thing is, I have read, that most women blame the travel and themselves for the m/c. usually an early m/c is due to a chromosonal problem with the baby and m/c was going to happen regardless. I travelled when I was just a month pg and asked the nurse basically your question. She told me there was nothing I could do or not do that would prevent a m/c at this point (outside, of course, something that you really shouldn't do like take drugs, etc.)
Im travelling by plane in Sept and ill be in my 2nd trimester by then.
I agree with Keyan about the whole not proven thing... But, now that I think about it (I had never related the two) - I had a m/c after finding out I was pregnant (vacation in FL) and ended up m/c 2 weeks after I flew home...
First, just remember that everyone is different and there is NO scientific evidence that flights can cuase m/c (I also asked my doc)...I also look in to the web and didn't find anything either...but in my case, I did travel while I was preggo and had a m/c. At the time I didn't know I was, I found out a week later and then a few days later the m/c...My doc told me that this didn't have anything to do w/ the m/c...but I totally understand your question..as I am TTC again at 9dpo and have a flight schedule for the 18 and don't know what I will do.
PS...while I was on the trip, I did go on rollercoasters too...sooo as for me..I have no idea if this had anything to do w/ the m/c or if it was a combination of factors