“The conception, namely the infusion of the soul, is believed to have taken place gently and blessedly, without original sin coming upon her; so that in the infusion of the soul she was also at the same time purified from original sin, adorned with God’s gifts, and received a holy soul poured into her by God, and thus from the first moment she began to live, SHE WAS FREE FROM ALL SIN. For before she lived, one might well say that she was neither in sin nor outside of sin, which applies only to souls and living humans.”  – (Emphasis mine)

This next quote is excerpted from this post: Luther on Luke 2 – Saint John’s Lutheran Church.

Then there are some who express opinions concerning how this birth took place, claiming Mary was delivered of her child while she was praying, in great joy, before she became aware of it, without any pains. I do not condemn these devotional considerations—perhaps they were devised for the benefit of simple-minded folk—but we must stay with the Gospel text which says she gave birth to him, and with the article of the creed which says “born of the Virgin Mary.” There is no deception here, but, as the words indicate, it was a real birth. Now we know, do we not, what the meaning of “to bear” is and how it happens. The birth happened to her exactly as to other women, consciously with her mind functioning normally and with the parts of her body helping along, as is proper at the time of birth, in order that she should be his normal natural mother and he her natural normal son. For this reason her body did not abandon its natural functions which belong to childbirth, except that she gave birth without sin, without shame, without pain, and without injury, just as she had conceived without sin. The curse of Eve, which reads: “In pain you shall bear your children” [Genesis 3:16], did not apply to her. In other respects things happened to her exactly as they happen to any woman giving birth …

I am talking about this so that we may have a foundation for our faith and that we let Christ be a natural human being, in every respect exactly as we are. Nor must we put him in a separate category as far as nature is concerned except where sin and grace are involved. In him and his mother nature was pure in all members and in all the functions of the members. No female body or one of its organs ever attained its natural function without sin, EXCEPT THIS VIRGIN. Here, for one time, God honored nature and its function. The more we draw Christ down into nature and into the flesh, the more consolation accrues for us. Therefore whatever is not contrary to grace should in no way be subtracted from his and his mother’s nature. The text clearly states and declares that she bore him, and that “he is born” is also proclaimed by the angels.

How could God have demonstrated his goodness more powerfully than by stepping down so deep into flesh and blood, that he does not despise that which is kept secret by nature, but honors nature to the highest degree exactly where it was brought into shame to the highest degree in Adam and Eve? … (Martin Luther, “The Gospel for Christmas Eve, Luke 2” in Luther’s Works (Fortress Press, 1974), LII, 7–31; emphasis mine)

Here’s another version taken from: Luther on the Virgin Birth of Christ.

Some argue as to how this birth took place, as if Jesus was born while Mary was praying and rejoicing, without any pain, and before she was conscious of it.  While I do not altogether discard that pious supposition, it was evidently invented for the sake of simple minded people.  But we must abide by the Gospel, that He was born of the virgin Mary.  There is no deception here, for the Word clearly states that it was an actual birth.

“It is well known what is meant by giving birth.  Mary’s experience was not different from that of other women, so that the birth of Christ was a real natural birth.  Mary being His natural mother and He being her natural Son. Therefore her body performed its functions of giving birth, which naturally belonged to it, except that she brought forth without sin, without shame, without pain and without injury, just as she had conceived without sin. The curse of Eve did not come on her, where God said: ‘In pain thou shalt bring forth children,’ Gen. 3:16; otherwise it was with her in every particular as with every woman who gives birth to a child. Grace does not interfere with nature and her work, but rather improves and promotes it”. (Christmas Day sermon, The Complete Sermons of Martin Luther, vol. 1.1-2, edited by John Nicholas Lenker, translated by John Nicholas Lenker and others [Baker Books, Grand Rapids, MI 2000] p. 140; emphasis mine)

FURTHER READING

LUTHER & MARY’S VIRGINITY REVISITED

LUTHER’S PRAISE OF MARY

LUTHER ON THE CATHOLIC CHURCH

MARTIN LUTHER, JAMES & NT CANON