It happened in those days, that an edict was issued by Augusto César, that everyone be registered.
2 This first census was done when Cyreneus was governor of Syria.
3 And they all went to be registered, each one to his city.
4 And Joseph went up from Galilee, from the city of Nazareth, to Judea, to the city of David, which is called Bethlehem, because he was of the house and family of David; 5 to be registered with Mary his wife, married to him, who was pregnant. 6 And it came to pass that while they were there, the days of her delivery were fulfilled.
7 And she gave birth to her firstborn son, and wrapped him in swaddling clothes, and laid him in a manger, because there was no place for them in the inn.
Luke 2: 1-7 New King James Version (RVR1960)

The birth of Jesus happened in a miraculous way. Jesus is the only one in everything, He was born without sin by a virgin birth, therefore he was free from the stain of sin.

Her mother a young maiden named Maria, was called blessed because God found grace in her among so many maidens but Maria was the chosen one. Maria's life suddenly changed when faced with a pregnancy while still a virgin, that is, she had never met a man.
How would she explain her situation to Jose, but God does not do anything incomplete, just as the angel Gabriel himself appeared to her to give her such news of this pregnancy. Jose did not know whether to secretly leave Maria because he did not want to harm her, since in those times it was a sin for a pregnant woman not to be married.
The angel Gabriel himself dealt with Jose clarifying the reason for such an event and why he should support Maria and take her as his wife.
Both Jose and Maria are blessed to have Jesus as their son for more than 30 years sharing with him and they overcame so many difficulties together, including his death that their own mother witnessed.