The Church teaches that the birth of Jesus Christ was virginal and miraculous.
“In union with the whole Church we celebrate that day (night)
when Mary without loss of her virginity gave this world its savior.
We honor her, the ever-virgin mother of Jesus Christ, our Lord and God.” (Eucharistic Prayer I, Communicantes for Christmas)
However, the Magisterium has not yet defined what constitutes a virgin birth. Here is my understanding, taken from my booklet, the Virginity of Jesus and Mary, which is also a chapter of my book, New Insights into the Deposit of Faith.
“The phrase without loss of her virginity means that Jesus left the womb of the Virgin Mary solely by a miracle of God and not in the usual way. Jesus went from being inside the womb to being outside the womb solely by means of the power of God. This is what is meant by a virgin birth; other explanations are insufficient and unacceptable.”
“Jesus Christ is perfect in all things, including His Perfect Virginity. God alone is the Father of Jesus Christ. God required the Holy Conception of Jesus Christ to be a miraculous Virgin Conception. Since Christ had a Virgin Conception, He must also have had a Virgin Birth, for the Virginity of Jesus Christ is entirely perfect in every way. The perfect, complete, and all-encompassing Virginity of Jesus Christ extends even to His perfect Virgin Conception and His perfect Virgin Birth. This teaching is trustworthy and true; it cannot be otherwise.
“God would not give the perfect-Virgin Jesus Christ a Virgin Conception within the womb of His mother, Mary, without also giving Him a Virgin Birth out of the womb of His mother, Mary. His Holy Conception was virginal and miraculous, therefore His Holy Birth was also virginal and miraculous. Every perfect Virgin must have both a Virgin Conception and a Virgin Birth. Jesus Christ is perfect in Virginity. Therefore, Jesus must have had both a Virgin Conception and a Virgin Birth, for without both His Virginity would not be perfect, complete, and all-encompassing. The Virgin Conception and Virgin Birth are joined by God and cannot be separated.
“The Virginity of Jesus Christ, the Son of God, is so perfect, complete, and all-encompassing that even His Holy Conception and His Holy Birth were entirely Virginal, occurring solely and entirely by a miracle of God and not in the usual way.”
by Ron Conte