Read this and answer the question. If the question is unanswerable, say "unanswerable".

The Perpetual Virginity of Mary asserts Mary's real and perpetual virginity even in the act of giving birth to the Son of God made Man. The term Ever-Virgin (Greek ἀειπάρθενος) is applied in this case, stating that Mary remained a virgin for the remainder of her life, making Jesus her biological and only son, whose conception and birth are held to be miraculous. While the Orthodox Churches hold the position articulated in the Protoevangelium of James that Jesus' brothers and sisters are older children of Joseph the Betrothed, step-siblings from an earlier marriage that left him widowed, Roman Catholic teaching follows the Latin father Jerome in considering them Jesus' cousins.

What doctrine asserts Mary's real and perpetual virginity before the act of giving birth to Jesus?
unanswerable