It's probably a little late to respond to this, but I'll chime in on the original question.

I'm 6 wks post-partum and while I stayed very active during the entire pregnancy (of more than 42 wks in my case) I don't think racing during the second trimester is a great idea (particularly if it's an activity that's new to you). The one thing I found over and over is that I had to be extremely flexible and constantly re-think activities to stay active throughout the pregnancy.

Re running- 24 wks is when I had to more or less give up (it had nothing to do with fitness- my abdominal muscles were just getting too loose and it's rather disconcerting to run with abdominal pain when you're pregnant).

Re biking- I stopped during the winter and found I couldn't resume it in the spring (at that point I was in my third trimester). It had nothing to do with balance or fitness- the issue is that there was enough extra weight hanging off my front that I had too much back pain (I couldn't sit in a regular chair for weeks and realized it was somewhat absurd to continue).

Re swimming- this actually worked well- but as one of the other posters pointed out- I had to be extremely careful about calories afterwards- I'd spend 1/2 an hour in the pool and feel great- as the pregnancy progressed I had less and less time to get fluids/calories into me afterwards without feeling like I was going to faint.

So in the end I found I had to constantly re-think what I was doing for reasons I hadn't predicted. I'd be concerned about combining all three in the second trimester in a race setting (especially if that setting is new to you).

Re shorts- Bornfit makes a maternity short- I used it a few times and liked it (but as above gave up riding sooner than I thought I would). I found that some of the regular shorts I had seemed to fit well even into my third trimester (the lower rise ones) BUT once I got on the bike and rode they put enough pressure on my abdomen to cause Braxton Hicks contractions (not a big deal but definitely interfered with the ride).

Re nutrition- I'd be really careful to make sure you eat/drink well after the swim (before you get on the bike) even if it takes more time.

Personally, I was determined to stay active during my pregnancy and felt I succeeded at that. I would encourage any woman to do the same. But I would also suggest you don't set your heart on any one particular activity and stay open minded about the fact that what works for you may change considerably between now and when you deliver.