Mary and God were the only ones who truly knew Mary was a virgin. Mary's knowledge, her truth that a miracle was inside her, necessitated an awareness that was easier for her to accept than those around her — and for generations following. The community they resided in was not inclusively God-fearing, faith-bearing individuals.
As this child developed inside Mary's womb, the realization become pretty evident to her. So much takes place physically and emotionally within a woman who is with child. Pregnancy is a reality for us. Mary knew she had not been with a man, and she knew that she was pregnant. These two contradictions clashed in an event that could only be deemed a miracle.
I have often thought about how God chose a virgin. I have also pondered the developmental stage of adolescence and how this played into the situation — albeit a different culture and time. Mary never knew a man, she was still innocent, and from Mary's perspective, this may have made the news easier to accept.
Often the older we get the more cynical we become. Mary was chosen by God, believed and brought the savior of all mankind into the world while loving him as her own. This is a complex circumstance to wrap one's mind around.
And then there is Joseph. What of Joseph? We read about his righteousness and his desire not to shame Mary, even though it looked like she had basically cheated on him. Yes, Joseph was required to believe a miracle as well. He did not have a fetus developing inside him. He did not know at first just what was taking place.