Import Duplicates

This is a general migrator question. I have multiple XML files from a wordpress site. This wordpress site is constantly being updated. My development site cannot keep up with the updates and when that site goes live and it posted for the public I'm going to do one final import.

My question is when I import will this create duplicates of the blogs? Or will the migrator check the database for the blog post and skip it?

Thanks for your help.