38 It was Mary who participated most intimately in this secret birth "of the body, the Church," (28) because the Holy Spirit gave fruitfulness to her virginity. St. Leo praises Mary as "the Lord's virgin, handmaid and mother," (29) "she who gave God birth" [ Dei genitrix ], (30) sea virgin for ever." (31)
Source: Aeterna Dei Sapientia (Vatican.va)