Sure, I wear a 38C when I'm not BFing/pregnant, when BFing/pregnant (like now), I'm usually in 40/42D once the initial OMG-boobs settle down, so I consider myself sort of medium sized with a large rib cage

So I don't know if my answers are as helpful, but I can't stand underwire while pregnant/BFing, it really hurts and as you probably know can lead to clogged ducts. I really go for the light support bras myself, but if you are looking for more support with no underwire, then something like it is what I would try:
http://www.bravadodesigns.com/shop/the-bliss-nursing-bra
If you can, go to somewhere that has lots of bras and just try on every nursing bra they have and see if you can find one without underwire that feels supportive. I'd hold off buying any probably yet, unless you find a nice stretchy one you like that will allow for growth, but at least you can have an idea of what kinds you liked for easier shopping closer to your due date and after.
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