This subject caught my attention after reading a passage in Sam Harris' book "The End of Faith".
"As many authors have observed, the numerous strands of Hebrew prophecy that were made to coincide with Jesus' ministry betray the aploogetics, and often poor scholarship, of the gospel writers.
The writers of Luke and Matthew, for instance, in seeking to make the life of Jesus conform to Old Testament prophecy, insist that Mary conceived as a virgin (Greek parthenos), harking to the Greek rendering of Isaiah 7:14. Unfortunately for fanciers of Mary's virginity, the Hebrew word alma (for which parthenos is an erroneous translation) simply means "young woman," without any implication of viginity. It seems all but certain that the Christian dogma of the virgin birth, and much of the church's resulting anxiety about sex, was the result of a mistranslation from the Hebrew." ¹
What does the WT have to say about this?
Messianic Prophecy.
Although the Hebrew word bethu?lah' means “virgin,” another term (?al?mah') appears at Isaiah 7:14: “Look! The maiden [ha??al?mah'] herself will actually become pregnant, and she is giving birth to a son, and she will certainly call his name Immanuel.” The word ?al?mah' means “maiden” and can apply to a nonvirgin or a virgin. It is applied to “the maiden” Rebekah before marriage when she was also called “a virgin” (bethu?lah'). (Ge 24:16, 43) Under divine inspiration, Matthew employed the Greek word par?the'nos (virgin) when showing that Isaiah 7:14 found final fulfillment in connection with the virgin birth of Jesus, the Messiah. Both Matthew and Luke state clearly that Jesus’ mother Mary was then a virgin who became pregnant through the operation of God’s holy spirit.—Mt 1:18-25; Lu 1:26-35. ²
Note that the WT uses NT examples, who would be trying to legitimize Jesus as the Messiah, and implied that al-mah should mean virgin in the case of Mary because another writer in the OT used it that way. Does that make sense?
¹ "The End of Faith". Sam Harris. pg 94-95.
² "Virgin". Insight on the Scriptures, Volume 2, page 1158.