I don't know if this helps or not but I was at the doctor 2 days ago and was reading a poster while waiting for the doctor that said "You Can Still Breastfeed If . . " and a whole bunch of reasons and one of them was if you have your nipples pierced so I don't think it would cause a problem
Here's some websites that have more information:
http://parenting.ivillage.com/newbor...,,3x0z,00.html http://www.piercing.org/faq/breastfeeding.html
Hope this helps =]