I recently read a fantastic quote from C. S. Lewis about the virgin birth:
"You will hear people say, ‘The early Christians believed that Christ was the son of a virgin, but we know that this is a scientific impossibility’. Such people seem to have an idea that belief in miracles arose at a period when men were so ignorant of the course of nature that they did not perceive a miracle to be contrary to it. A moment’s thought shows this to be nonsense: and the story of the Virgin Birth is a particularly striking example. When St Joseph discovered that his fiancée was going to have a baby, he not unnaturally decided to repudiate her. Why? Because he knew just as well as any modern gynecologist that in the ordinary course of nature women do not have babies unless they have lain with men. No doubt the modern gynecologist knows several things about birth and begetting which St Joseph did not know. But those things do not concern the main point–that a virgin birth is contrary to the course of nature. And St Joseph obviously knew that. In any sense in which it is true to say now, ‘The thing is scientifically impossible’, he would have said the same: the thing always was, and was always known to be, impossible unless the regular processes of nature were, in this particular case, being over-ruled or supplemented by something from beyond nature. When St Joseph finally accepted the view that his fiancée’s pregnancy was due not to unchastity but to a miracle, he accepted the miracle as something contrary to the known order of nature. All records of miracles teach the same thing." —CS Lewis (from, Miracles)It’s quite a legitimate point. Look back at the gospel accounts of this. When Mary was told what was going to transpire, she was not quick to just accept it. She was just as incredulous as anyone ought to be:
“In the sixth month the angel Gabriel was sent from God to a city of Galilee named Nazareth, to a virgin betrothed to a man whose name was Joseph, of the house of David. And the virgin's name was Mary. And he came to her and said, "Greetings, O favored one, the Lord is with you!" But she was greatly troubled at the saying, and tried to discern what sort of greeting this might be. And the angel said to her, "Do not be afraid, Mary, for you have found favor with God. And behold, you will conceive in your womb and bear a son, and you shall call his name Jesus. He will be great and will be called the Son of the Most High. And the Lord God will give to him the throne of his father David, and he will reign over the house of Jacob forever, and of his kingdom there will be no end." And Mary said to the angel, "How will this be, since I am a virgin?" And the angel answered her, "The Holy Spirit will come upon you, and the power of the Most High will overshadow you; therefore the child to be born will be called holy—the Son of God. And behold, your relative Elizabeth in her old age has also conceived a son, and this is the sixth month with her who was called barren. For nothing will be impossible with God." And Mary said, "Behold, I am the servant of the Lord; let it be to me according to your word." And the angel departed from her.”Luke 1:26-38 ESV
As Lewis points out, Joseph was also not easily convinced:
“Now the birth of Jesus Christ took place in this way. When his mother Mary had been betrothed to Joseph, before they came together she was found to be with child from the Holy Spirit. And her husband Joseph, being a just man and unwilling to put her to shame, resolved to divorce her quietly. But as he considered these things, behold, an angel of the Lord appeared to him in a dream, saying, "Joseph, son of David, do not fear to take Mary as your wife, for that which is conceived in her is from the Holy Spirit. She will bear a son, and you shall call his name Jesus, for he will save his people from their sins." All this took place to fulfill what the Lord had spoken by the prophet: "Behold, the virgin shall conceive and bear a son, and they shall call his name Immanuel" (which means, God with us).”Matthew 1:18-23 ESV
The fact is that EVERYONE understood what it meant that Mary was pregnant and not yet married. It took some angelic convincing to bring them around to seeing this as an exception to the rule. Miracles are called miracles because even in biblical times they were out of the ordinary.
I tried to look up the number of miracles in the entire Bible and there were apparently 37 performed by Jesus, but the most extensive list of Old Testament miracles I could find contained 91. 27 of those are directly related to Moses. So over a period of about 4000 years (Or more depending on how you read it) we are talking about 130 miracles? Even if they were spread out evenly and not bunched around a couple of figures or events (The Exodus and Jesus Christ), that’s about 1 every 31 years. Not exactly a daily event. If you remove Jesus and Moses from the picture as outliers you are looking at one every 74 years. (Even then they weren't evenly spread, mostly limited to specific prophets, Judges, etc.)
The point here is, people didn't find a miracle around every corner. Though not necessarily scientifically advanced, they weren't completely ignorant of the course of nature. The virgin birth was viewed as a miracle not due to the ignorance of the early church but rather due to their knowledge.
