Mary conceived by the Holy Spirit without the cooperation of man. (De fide)
Mary bore her Son without any violation of her virginal integrity. (De fide)
After the Birth of Jesus, Mary remained a Virgin. (De fide)
Catechism of the Catholic Church
A Bogus Greek Argument against Mary's Perpetual Virginity by Ronald K. Tacelli, S.J.
The Key to Understanding Mary by James Akin
How Did St. Jerome Defend Mary's Perpetual Virginity? by James Akin
How Would Mary's Virginity Have Been Understood in a First Century Jewish Context? by James Akin