"She is blessed above all other women, not only because she gave birth without labor, pain, and injury to herself, not as Eve and all other women, but because by the Holy Spirit and without sin she became fertile, conceived, and gave birth in a way granted to no other woman." - Martin Luther, Personal Prayer Book 1521 (and reprinted throughout his life), AE 43:40.
"Now, although Mary was not required to do this - the law of Moses having no claim over her, for she had given birth without pain and her virginity remained unsullied - nevertheless, she kept quiet, and submitted herself to the common law of all women and let herself be accounted unclean. She was without doubt a pure, chaste virgin before the birth, in the birth, and after the birth, and was neither sick nor weakened from the birth, and could certainly have gone out of the house after giving birth, not only because of her exemption from the Law, but also because of the uninterrupted soundness of her body." - Martin Luther, preached at the parish church in 1541 on the Eve of the Circumcision, House Postil III:256.
"He employed this mode of presence when He left the closed grave and came through the closed door, in the bread and wine in the Supper, and, as people believe, when He was born in His mother." 1577, SD VII:100
"He showed His divine majesty even in His mother's womb, because He was born of a virgin without violating her virginity. Therefore, she is truly the mother of God and yet has remained a virgin." 1577, SD VIII:24