Mary was conceived without original sin. This is an official dogma of the Catholic church that Mary was conceived without sin.

Catholics believe that Saint John the Baptist was consecrated in the womb, by the Holy Spirit and was born without sin, but this is simply a belief, not a dogma of the church. Here are a couple of links to check out, but let’s not split hairs about this. Mary’s Immaculate Conception is a dogma of our faith, but it is also a commonly held belief that Saint John the Baptist was sanctified by the Holy Spirit in the womb, (similar to being baptized). How could Saint John the Baptist, baptize others if he still had original sin on his own soul? Jesus sanctified John in the womb, so that he would have the ability and authority to baptize others during his ministry.

http://www.ewtn.com/vexperts/showmessage_print.asp?number=312243&language=en

http://catholicism.about.com/od/beliefsteachings/p/Who-Was-Born-Without-Original-Sin.htm

http://jimmyakin.com/2004/12/john_the_baptis.html

http://www.catholicforum.com/forums/showthread.php?50828-Baptism-And-Saint-John-The-Baptist