The Church (both East and West) teaches, and has always taught that our Lord's Birth was a mystery just as His Incarnation is. We do not usually go into "fine" details of just "how" mysteries of God happen.
The Church does teach that the birth canal remained closed and her virginity (the "seal") was preserved. You are free to use tour imagination to "figure out" how one can be born "naturally" (as the Protestants believe) through a closed birth canal without violating someone's virginity, but it is not a "natural" birth.