Ambrose of Milan — as excerpted in the Catena Aurea on Luke 1:56

“Now it was not only for the sake of friendship that she abode so long, but for the increase also of so great a prophet. For if at her first coming the child had so far advanced, that at the salutation of Mary he leaped in the womb, and his mother was filled with the Holy Spirit, how much must we suppose the presence of the Virgin Mary to have added during the experience of so long a time? Rightly then is she represented as having shewn kindness to Elisabeth, and preserved the mystical number.”