I found this article on Lutheran Marian Theology online and find it to be fairly accurate in dealing with a controversial topic. The article treats different well-known teachings on Mary and how they are viewed by Lutheran groups and their theologians.
For example, Lutherans will not be surprised to see that their church bodies do not teach such things as the perpetual virginity of Mary nor prayer to Mary and the saints. They may be surprised to learn that Martin Luther held to the perpetual virginity and Immaculate Conception of Mary and that he called her the "Mother of God." He did not have much to say about the Assumption of Mary except that it was not in the Bible. Luther had a high view of the Magnificat and this canticle has been retained in Lutheran liturgical practice to this day. As with Luther the perpetual virginity of Mary was confessed in the Lutheran confessional writings and held by such prominent Lutheran theologians as Franz Pieper.
They may also be surprised to learn that the perpetual virginity of Mary is still held by some Lutherans today. Adherence to this teaching is not mere exaltation of Mary although it may appear as such at first glance. She is clearly "blessed among women" and above the saints. Her unique role in God's salvation, her relationship with her son (the Son of God) and her humble example do indeed set her apart from others. Rather this teaching is related to and centered on a high view of the person and work of Jesus Christ and the Incarnation. With this in mind the teaching of the perpetual virginity of Mary is easier to fathom as one of God's mysteries of salvation.