However, Jesus was conceived "supernaturally" and it is not unreasonable to say that He was born supernaturally. There was no "seed" uniting with Mary's ovum, but an ineffable God covering Himself with her flesh and fashioning a Child the way God the father fashioned Adam, except this time it was flesh and not clay.
The painlessness of her birth is probably tied to the Catholic belief that she was, through Immaculate Conception, a pre-Fall second Eve and therefore spared the "curse" of painful births through the ancestral sin.
I have never heard of this account before. I have always thought that the Spirit "produced" the necessary genetic material and caused it to unite with Mary's egg, (without any "union" in the human sense, of course). But you're saying that God just "zapped" a fertilized embryo into Mary's womb? So, Jesus did not have Mary's blood type or any of her DNA, that kind of thing? If true, that would definitely seem to throw new light onto the "birth-giver of God" vs. "Mother of God" debate.