See the Bible.
Luke 1:39-56
[39] At that time Mary got ready and hurried to a town in the hill country of Judea, [40] where she entered Zechariah’s home and greeted Elizabeth. [41] When Elizabeth heard Mary’s greeting, the baby leaped in her womb, and Elizabeth was filled with the Holy Spirit. [42] In a loud voice she exclaimed: “Blessed are you among women, and blessed is the child you will bear! [43] But why am I so favored, that the mother of my Lord should come to me? [44] As soon as the sound of your greeting reached my ears, the baby in my womb leaped for joy. [45] Blessed is she who has believed that what the Lord has said to her will be accomplished!”
[46] And Mary said:
“My soul glorifies the Lord
[47] and my spirit rejoices in God my Savior,
[48] for he has been mindful
of the humble state of his servant.
From now on all generations will call me blessed,
[49] for the Mighty One has done great things for me —
holy is his name.
[50] His mercy extends to those who fear him,
from generation to generation.
[51] He has performed mighty deeds with his arm;
he has scattered those who are proud in their inmost thoughts.
[52] He has brought down rulers from their thrones
but has lifted up the humble.
[53] He has filled the hungry with good things
but has sent the rich away empty.
[54] He has helped his servant Israel,
remembering to be merciful
[55] to Abraham and his descendants forever,
even as he said to our fathers.”
[56] Mary stayed with Elizabeth for about three months and then returned home.
Sorry, didn’t realize the biology would be over your head.