This refers to conceiving where the purest thoughts reign on both sides with the sexual instinct being only an adjunct but not the principal feeling. The main reason for the coming together of the couple must be pure love of the soul for each other and not lust.
This is immaculate conception in the physical sense. Immaculate conception in the spiritual sense is something entirely different and is not to found among mankind. It refers to a direct Incarnation of a Part of the Light Itself; a direct connection between the Light Itself and the developing physical body in the womb of the woman carrying the baby.
It is immaculate because there is no break at all in the connection from the Light and the developing physical body in the womb. This is what makes the event spiritually immaculate. With human beings, it is entirely different. We have burdened ourselves with so much guilt that the connection to the Light in many cases is completely cut off and as such our incarnations could never be immaculate. What makes an incarnation spiritually immaculate is the degree of connection of the incarnating individual to the Light. What make it physically immaculate is that the physical act itself is not brought about through lust for each other but by pure spiritual love.
In the case of Jesus, being out of God, His connection to the Light was firm and unbroken, hence His spiritual incarnation was immaculate. What also made the incarnation of Jesus physically immaculate was that His earthly parents met under the most pure spiritual love for one other. All the conditions were therefore fulfilled for Jesus and there was never any need to change the Laws of Creation for this event.
So there was no question of Mary suddenly getting pregnant by some sort of miracle. There was no need for that. Jesus’ conception was guaranteed immaculate both spiritually and physically because of what has been mentioned above.