According to the Church Fathers conception would have occurred without concupiscence or loss of virginity. They speculated "how," but were unanimous that it was definitely not as it is after the Fall, involving concupiscence and the loss of virginity.

Interesting. Without concupiscence is at least conceivable in the realm of nature, perhaps preternatural. Without loss of virginity is miraculous. I’d like to learn more about this.

Here is a very brief explaination: The Fathers' consensus is that Adam and Eve maintained perfect virginal integrity in Eden and the new Adam and new Eve (Our LORD & Our Lady) are Perpetual Virgins, thus logically concluding that Perpetual Virginity was the original intent for Adam and Eve. Patristic speculations enter regarding the precise mode of Edenic conception.
Bl. Catherine Emmerich reveals that the Immaculate Conception of Our Lady was Supernatural and was the originally intended Edenic mode.
The critical error of post-Patristics is assuming the mode of conception would have necessarily been without concupiscence yet purely natural.