"there is no explicit prohibition of abortion in either the Old Testament or New Testament
Of course there is, in both. The prohibition against murder. Also:
Jeremiah 1:5
Before I formed thee in the belly I knew thee; and before thou camest forth out of the womb I sanctified thee, and I ordained thee a prophet unto the nations.
Judges 13:3-5
3 And the angel of the Lord appeared unto the woman, and said unto her, Behold now, thou art barren, and bearest not: but thou shalt conceive, and bear a son.
4 Now therefore beware, I pray thee, and drink not wine nor strong drink, and eat not any unclean thing:
5 For, lo, thou shalt conceive, and bear a son; and no razor shall come on his head: for the child shall be a Nazarite unto God from the womb: and he shall begin to deliver Israel out of the hand of the Philistines.
Luke 1:42-45
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:
And she spake out with a loud voice, and said, Blessed art thou among women, and blessed is the fruit of thy womb.
And whence is this to me, that the mother of my Lord should come to me?
For, lo, as soon as the voice of thy salutation sounded in mine ears, the babe leaped in my womb for joy.
The baby in the womb is alive and God knows him or her from the moment they are created. Some are called even before birth to be consecrated to God.