The dress has been altered to be strapless to give it a beautiful look. I love, love, love this dress. The buttons down the back were a big part of the selling point for me. Pronovias is an Italian designer so it's listed as a size 4 but, FITS like a US size 2. When the dress came in, I had to lose weight for it haha. With that said, I did lose the appropriate weight for it but no, I did not stretch it at all, so there's no worry about that!
You can see the up-close view of the material and it's original design with the straps here: http://www.bestbridalprices.com/images/pronovias/large/Diamante.html