§490
Creed › … › Paragraph 2. "Conceived by the Power of the Holy Spirit and Born of the Virgin Mary"
The Immaculate Conception
To become the mother of the Saviour, Mary "was enriched by God with gifts appropriate to such a role." The angel Gabriel at the moment of the annunciation salutes her as "full of grace". In fact, in order for Mary to be able to give the free assent of her faith to the announcement of her vocation, it was necessary that she be wholly borne by God's grace.
Source: Catechism of the Catholic Church (Vatican.va)