Clustered miracles

Accounts of the virgin birth occur in two of the four Gospels. That's not surprising, considering the fact that only two of the four Gospels even have nativity accounts. 

The virgin birth has a litmus test of orthodoxy. Unbelievers regard the virgin birth has a transparent cover story for a prenuptial scandal. 

I presume most of Mary's relatives and neighbors were initially skeptical. But the credibility of the virgin birth doesn't occur in isolation. Suppose you were one of Mary's skeptical in-laws. You think she had premarital sex. Indeed, that's what Joseph thought. He intended to divorce her.

But then Joseph abruptly changes his mind. He tells you about a revelatory dream he had. 

Then Elizabeth becomes pregnant, even though she's well past childbearing years. After Zechariah recovers his speech, he talks about an angelic apparition. 

Then shepherds say angels appeared to them, heralding the birth of Jesus. 

Later, the Magi arrive. 

Maybe you notice the odd behavior of a "star". 

Then Joseph claims to have another revelatory dream, warning him of danger, so he skips town with Mary and the Christchild. Shortly thereafter, soldiers sent by Herod massacre all the young boys. 

Maybe you near rumors about Anna and Simeon in the Temple.

Finally, Jesus grows up to be a renown exorcist and miracle-worker.

Mary's explanation, which struck you as initially highly implausible, becomes highly plausible in light of so many other miracles clustering around the person of Jesus.