I believe that the baby can not get it in the womb, or the chances are very low, the problem is that they get it at the birthing process. As for treatment, they can treat the mother so her viral load goes down and the chances are lower.
I went and looked up if C-section might reduce the chance of HIV but there's lack of evidence to it.
http://www.uwgb.edu/bauera/angiesweb/BOW/SLProjects02/Treague/web%20page%201/pregnancy.htm. It could be a technique issue though.