"Perpetual virginity" is very different from "intact, physical" virginity after natural childbirth which strikes many Christians as ludicrous.
-A8
In other words, in those times the claim that someone remained a virgin perpetually was not intended to claim only that such a person never had sexual relations. It was also an implicit claim about their physical integrity. So, for example, in a sermon of the Council of Ephesus, it is said: "After giving birth, nature knows not a virgin". That's 431 AD.
And Augustine says (Sup. Joan. Tract. 121): "To the substance of a body in which was the Godhead closed doors were no obstacle. For truly He had power to enter in by doors not open, in Whose Birth His Mother's virginity remained inviolate."
-A8