To argue the case from the Bible, I thought a key passage to point to was Psalm 139.
Recently I saw the title of a message by John Piper which refered to John the Baptist. Hmmm.
John the Baptist in-utero leaps for joy at the sound of Mary (and Jesus in-utero).
Luke 1:39-45 (ESV)
In those days Mary arose and went with haste into the hill country, to a town in Judah, and she entered the house of Zechariah and greeted Elizabeth. And when Elizabeth heard the greeting of Mary, the baby leaped in her womb. And Elizabeth was filled with the Holy Spirit, and she exclaimed with a loud cry, "Blessed are you among women, and blessed is the fruit of your womb! And why is this granted to me that the mother of my Lord should come to me? For behold, when the sound of your greeting came to my ears, the baby in my womb leaped for joy. And blessed is she who believed that there would be a fulfillment of what was spoken to her from the Lord."