With all the news about radiation and the nuclear catastrophe in Japan, I thought it appropriate to visit this topic. Firstly pregnant women should not get unduly alarmed. Although air travel has been on the increase, there does not appear to be an increase in the number of children with abnormalities or developing leukaemia. air travel exposes the foetus to cosmic radiation. The amount of radiation is low, less than that of a normal chest xray. however, the longer the exposure the greater the potential risk. Long haul flights (>4 hours) would increase the risks. Foetal cells are at greater risk of damage than adult cells. In the first trimestor and up to 18 weeks, the risks would be that of miscarriage, damage to the chromosomes resulting in foetal abnormalities especially the brain. after 28 weeks, the foetus is fully formed. The risks then is that of cancer eg leukaemia in the future.
To avoid the potential risks to your baby, it would therefore be prudent not to travel up to 18 weeks, and if you have to travel, confine it to short haul flights. Minimise the number of flights overseas throughout your pregnancy. http://www.safety.duke.edu/radsafety/fdose/fdrisk.asp