The Immaculata had conceived Our Precious Lord by the power of the Holy Spirit. During The Visitation, she learns that St. Elizabeth is pregnant with John The Baptist by her husband Zebadiah.
From the Gospel of Luke 1:39-56:
39 And Mary arose in those days, and went into the hill country with haste, into a city of Juda; 40 And entered into the house of Zacharias, and saluted Elisabeth. 41 And it came to pass, that, when Elisabeth heard the salutation of Mary, the babe leaped in her womb; and Elisabeth was filled with the Holy Ghost: 42 And she spake out with a loud voice, and said, Blessed art thou among women, and blessed is the fruit of thy womb.
43 And whence is this to me, that the mother of my Lord should come to me? 44 For, lo, as soon as the voice of thy salutation sounded in mine ears, the babe leaped in my womb for joy. 45 And blessed is she that believed: for there shall be a performance of those things which were told her from the Lord. 46 And Mary said, My soul doth magnify the Lord,
47 And my spirit hath rejoiced in God my Saviour. 48 For He hath regarded the low estate of his handmaiden: for, behold, from henceforth all generations shall call me blessed. 49 For He that is mighty hath done to me great things; and holy is his name. 50 And His mercy is on them that fear Him from generation to generation. 51 He hath shewed strength with His arm; He hath scattered the proud in the imagination of their hearts. 52 He hath put down the mighty from their seats, and exalted them of low degree. 53 He hath filled the hungry with good things, and the rich He hath sent empty away. 54 He hath helped His servant Israel, in remembrance of His mercy; 55 As He spake to our fathers, to Abraham, and to his seed for ever. 56 And Mary abode with her about three months and returned to her own house.
St. Luke compares Our Lady to The Ark of the Covenant.