First time lady triathletes - sports bra?

I am not a big breasted lady but the support in those tri suits are not enough, at least for me. So I wear a sports bra under the tri suit.For those not wanting to invest in a tri suit then have them wear a support bra that can look like a binki top for the swim and then during T1 they can put a top on. I have also seen where others will wear their swim suit the entire time and just put shorts and a top over it. It really is a preference of what you want to wear and how much support you want.

Really depends on the woman's size and preference, and the tri-suit. Some tri suits have more support than others. Many smaller women will be able to just use a tri-suit with a good built-in bra; most larger women prefer some kind of sports bra under the suit. They typically wear it for the whole race. If someone didn't want to buy a tri suit they could just use a sports bra as a top for the swim and then put on a shirt or singlet in transition. I've never seen anyone put a bra on in transition. Hard to envision how you could do it at all, much less discreetly, unless it was an iron-distance event and had changing tents!

I race in a sport bra and tri shorts/briefs. No other top.

I always have to wear a sports bra under my tri top. For the bigger chested women I recommend a bra from Moving Comfort that has under wires and the cups are made of a fine mesh, so it dries really fast.  I did my first tri in a regular sports bra  under my tri top which was still wet from the pool  after the run and the finish line photo proofed that it did not offer adequate support after having been wet/stretched for more than 1 hour  

I'm a 32A and I'm fine with just my tri top and its built-in support. It's harder than heck to get into and out of, though...