I had been wearing a 38C in this bra and loved it.  I am a runner and it did a great job keeping things where they needed to be.  Then I got pregnant.  As my breasts got bigger the 38C was getting to be just too small, both around my ribs and in the cups, so I went up a size in both measurements.  I found the 40D to be too big in the cups but the 38C was too small in the cups.  Returns are easy, so if the bra doesn't fit well, that's an option.  But it is frustrating that the D seems so much bigger than the C because now neither one fits properly.