I view the Bible as being 100% truthful and reliable...however...it doesn't always report 100% of what actually happened. At times, it uses figures of speech and poetic language and just plain leaves some things out.
For example, what really happened between Luke 1:26-56 and Matthew 2:18?
Following the angel Gabriel's announcement to Mary that she would give birth to the Messiah, and Mary's hasty, three-month visit with her kinswoman, Elizabeth, she returned to Nazareth and her betrothed, Joseph.
"Joseph?" Mary inquired, as she entered the carpenter's shop.
"Is that the voice of my turtle dove?" laughed Joseph as he picked Mary up and swung her around in joy.
"Careful, you glorified lumberjack."
Joseph was a little confused about needing to be careful, so Mary continued: "I've got some wonderful news, oh hubby-to-be! I am expecting a child."
"That's a wonderful, positive attitude, my basket of flower petals. I, too, expect that our God will be gracious and grant to us the blessing of being parents." (Joseph was not the sharpest chisel in the toolbox.)
"You don't understand, my muscular ox. I am, even now, at this very minute, expecting a child."
Joseph tilted his head to one side, squinted, and slowly said, "Yea, verily...me, too."
Mary slipped her hands up Joseph's arms and cupped his face. "Let me speak plainly, oh He Who Is Strong of Arm and Thick of Skull. I'm preggers."
The light dawned excruciatingly slowly in the carpenter's mind: "Heyyyyy...what were you doing for the last three months, anyway? I thought you were visiting your cousin Elizabeth. Is there something in the water up there?"
"Joseph," Mary calmly interjected, "I am not pregnant by the effort of any man. God has placed this child within me."