Whether it is classified as strictly revealed or a necessary consequence of the a truth strictly revealed–both the immaculate conception and perpetual virginity (before, during, and after birth)–it is certainly taught by the Church that she was without pain:
Roman Catechism (after discussing how Christ was born without injury to Mary’s virginity):
To Eve it was said: In sorrow shalt thou bring forth children. Mary was exempt from this law, for preserving her virginal integrity inviolate she brought forth Jesus the Son of God without experiencing, as we have already said, any sense of pain.
One of the preface prayers currently approved for use for Masses of the Blessed Virgin specifically says (and this is on point with regard to the pain shown in Revelation):
“…she was to be a partner in his passion, and she who had given him birth without the pains of childbirth, was to endure the greatest of pains in bringing forth to new life the family of your Church.”
Evening Prayer for Friday in the Little Office says the same:
“She conceived and gave birth to a son without pain…”
Finally, from the Summa:
On the contrary, Augustine says (Serm. de Nativ. [Supposititious), addressing himself to the Virgin-Mother: “In conceiving thou wast all pure, in giving birth thou wast without pain.”
I answer that, The pains of childbirth are caused by the infant opening the passage from the womb. Now it has been said above (28, 2, Replies to objections), that Christ came forth from the closed womb of His Mother, and, consequently, without opening the passage. Consequently there was no pain in that birth, as neither was there any corruption; on the contrary, there was much joy therein for that God-Man “was born into the world,” according to Isaiah 35:1-2: “Like the lily, it shall bud forth and blossom, and shall rejoice with joy and praise.”
Reply to Objection 1. The pains of childbirth in the woman follow from the mingling of the sexes. Wherefore (Genesis 3:16) after the words, “in sorrow shalt thou bring forth children,” the following are added: “and thou shalt be under thy husband’s power.” But, as Augustine says (Serm. de Assumpt. B. Virg., [Supposititious), from this sentence we must exclude the Virgin-Mother of God; who, “because she conceived Christ without the defilement of sin, and without the stain of sexual mingling, therefore did she bring Him forth without pain, without violation of her virginal integrity, without detriment to the purity of her maidenhood.” Christ, indeed, suffered death, but through His own spontaneous desire, in order to atone for us, not as a necessary result of that sentence, for He was not a debtor unto death.