Matthew alleges that Jesus’ birth fulfilled a prophecy. Per Mt. 1:22-23:
All this took place to fulfill what the Lord had said through the prophet: “The virgin will be with child and will give birth to a son, and they will call him Immanuel”—which means, “God with us.” (NIV)
Did this fulfill an Old Testament prophecy? Let’s examine the context of the original verse in the Book of Isaiah. King Ahaz of Judah is concerned about aggression from the kings of Aram and Israel and he gets some advice from a prophet. Per Isaiah 7:14-16:
Therefore the Lord himself will give you a sign: The virgin will be with child and will give birth to a son, and will call him Immanuel. He will eat curds and honey when he knows enough to reject the wrong and choose the right. But before the boy knows enough to reject the wrong and choose the right, the land of the two kings you dread will be laid waste. (NIV)
Could this passage have been intended to refer to Jesus? It appears merely to be about people living at the time, and in fact in Isaiah 8:3 a male child is born. Jesus was never called Immanuel. As the Son of God it does not make sense to suggest that Jesus was ignorant of right and wrong. To support the claim that Jesus fulfilled this prophecy it would be necessary to demonstrate that he was born of a virgin, and the only evidence that this occurred is in the statements of Matthew and Luke.
Additionally, this prophecy is based on a mistranslation from Hebrew. As the Biblical inerrancy site 100propchecies.org explains:
[Non-Christian scholars] say that the Hebrew word “almah,” which is the word that Christian Bibles often translate as “virgin,” actually means “young maiden.” It is true that “almah” means “young maiden,” however, the Bible never uses the word to refer specifically to a married woman.
In reality, with the exception of the Young’s Literal Translation version, neither is it remotely true that every instance of “almah” in the Bible is translated as “virgin.” Proverbs 30:18-19 in particular is translated, in the New International Version, as follows:
There are three things that are too amazing for me, four that I do not understand: the way of an eagle in the sky, the way of a snake on a rock, the way of a ship on the high seas, and the way of a man with a maiden.
It would seem problematic to substitute “virgin” in this case.
If, however, one were to assume the woman in the Isaiah passage were a virgin then that would necessitate explaining two miraculous conceptions.