I just read a really good book recently called "Runners World guide to Running and Pregnancy" by Chris Lundgren. It is the first book on exercise while pregnant that actually considers the women who view exercise as more than a brisk walk or aqua aerobics class. I can't remember if there is anything in it specifically regarding racing but it does talk about varying your effort and intensity depending on how your pg progresses which would be relevant to racing. Personally I think racing would be fine as long as you are training and know how to limit your effort appropriately in a race situation (ie. Paula Radcliffe). I am 7months pg and considering entering a 2km ocean swim in 2 weeks - which some people would say is stupid but I know what to expect and have been regularly swimming that far in my training.