yes, i heard this too, after my DD was born! The bra fitting lady chastised me for not geting fitted at 12 weeks pregnant!

The reason for it, I believe, is that it could damage the breast tissue, or lead to blocked ducts....or something like that (even in pregnancy). I am a D cup, and used to be very pro-underwire...I am now anit-bra (LOL)...they are so expensive (particularly nursing bras) and after a few washes are uncomfortable...but I found some comfy ones for $16, they probably are not flattering, but they are comfy. MOre like a singlet or sports bra I guess.

I found an interesting site when I was trying to find out about this question yonks ago...Why women wear bras