The doctrine of the Immaculate Conception of Mary is not to be confused with the doctrine of the Virgin Birth of Jesus Christ. The latter is a biblical teaching whereas the former is a concocted teaching based on speculation, popularity, and Papal authority.

The doctrine of the Immaculate Conception of Mary asserts that she was miraculously preserved from the taint of original sin, but not that she herself was virgin-born.

In 1854 Pope Pius IX officially decreed the doctrine of The Immaculate Conception. The doctrine was broached about 1140 but was opposed by Thomas Aquinas and other catholic theologians as being opposed to the doctrine of Original Sin. In the following centuries it continued to be defended until finally affirmed by the Pope in 1854. [CHURCH HISTORY, Hassell; pgs. 302, 330, 435, 582, 588]

The roots of the doctrine go back to Constantinople. In the 5th century a controversy arose over the term “theotokos” as a title for the Virgin Mary. At the time the term meant “God-bearing one” and was only intended to affirm the deity of Jesus Christ. Theologians were attempting to explain how Jesus’ flesh could be real but not tainted by sin. In order to emphasize the holiness of Christ, it became customary to exalt the holiness of the one who bore him in her womb. Later the term came to be a title of honor for Mary.

“Although the New Testament refers to Jesus as having brothers and sisters, pious tradition began to see these as collateral relatives or perhaps Joseph’s children by an earlier marriage; it was argued that Mary remained a virgin all her life; finally, it was even stated that she had delivered Jesus without injury to her virginity, i.e., miraculously, without rupturing the hymen.” [HERESIES; pg. 173]

Nestorius, patriarch of Constantinople, observed the beginnings of this development and warned against making the Virgin into a goddess. He preferred the term “Christotokos” which was quite orthodox but was unpopular with those who emphasized the deity alone and was resented by those devoted to the growing cult of Mary. For the first time, growing popular piety was beginning to play a role in deciding a major theological issue.
[unless otherwise noted all references are from the book, Heresies, by Harold O. J. Brown, pg 172-174]