Was there really a virgin birth in the Bible? The answer is yes and no, in that order.
The virgin birth of Jesus, which is a cornerstone of Christianity (and, as it happens, is important in Islam as well), is described in clear terms in the Gospels of Matthew and Luke. Matthew (Matt 1:18) says that Jesus Christ is born to Mary, who becomes pregnant before having sex with her betrothed, Joseph. And Luke (Luke 1:26-35) explains that Mary, a virgin, conceives even though she is a virgin. That is the yes part of the answer. Though the implications are, obviously, controversial, the text is straightforward.
The more interesting potential virgin birth, though, comes from Matthew's explanation in Matt 1:22-23. There the text says that the virgin birth of Jesus took place to "fulfill" the prophecy that "the virgin shall conceive and bear a son, and they shall name him Emmanuel." Matthew is paraphrasing Isa 7:14.
But he is quoting a mistranslation. The original Hebrew text of Isa 7:14 is not about a virgin. Rather, the Hebrew used to describe the woman in Isa 7:14 is almah, a word that means "young woman." But then the Septuagint, an early translation of the Hebrew Bible into Greek, took the Hebrew almah and rendered it as the Greek parthenos, which means "virgin."
This inadvertent shift from "young woman" to "virgin" is typical of the Septuagint, and it occurs elsewhere, too. For instance, the Hebrew text of Gen 24:16 describes Rebecca as a "young woman [who was] a virgin" (using na'arah, another Hebrew word for "young woman"). But the Greek in the Septuagint changes that into "a virgin [who was] a virgin." These errors are not surprising, because the Septuagint translators tended not to focus as closely on individual words as some modern readers might like.
In most contexts, calling a "young woman" a "virgin" in the days of the Septuagint would be only a minor translation mistake, hardly even noteworthy, because most young women were virgins, and most female virgins were young women. In modern terms, it would be like mixing up "high schooler" and "teenager"—imprecise perhaps, but good enough for most purposes.
But in one situation, obviously, turning a young woman into a virgin rises to the level of a serious gaffe. And that's when the young woman is pregnant. This is how the Septuagint, through lack of precision, turned an ordinary birth into a virgin birth.
And this is the “no” answer to the question about whether the Bible includes a virgin birth. Isa 7:14 is not about a virgin birth except through mistranslation.
Matthew was writing in Greek, so he quoted the Greek mistranslation of Isa 7:14, using it to match his own virgin-birth description regarding Jesus. As it happens, Matthew almost certainly knew that the two texts matched only in Greek. He wouldn't have cared. His focus was on what Isaiah could be made to mean in a new context, not what it meant in its original context. This is why Matthew didn't care about other material mismatches between his writings and the text he quotes from Isaiah: for instance, the child born in Isaiah was named Emmanuel, not Jesus.
This kind of imprecision was common in early Christianity and Judaism. If our modern sensibility balks at Matthew's explanation based on mistranslation and partial matching, the whole issue only highlights how much the very notion of what it means to read the Bible has evolved.
[Adapted from Chapter 8 of And God Said: How Translations Conceal the Bible's Original Meaning]