From The Encyclopedia of Mormonism
Author: Lamb, Connie
Immaculate conception is the belief of some Christians that from her conception in her mother's womb, Jesus' mother was free from original sin. Original sin holds that Adam's sinful choice in the Garden of Eden, made for all his descendants, led to a hereditary sin incurred at conception by every human being and removed only by the sacraments of the church. From this view arose the concept of Mary's immaculate conception. By a unique grace, Mary was preserved from the stain of original sin, inheriting human nature without taint in order that she be a suitable mother for Jesus. This teaching was defined as obligatory dogma by Pope Pius IX in 1854.
Latter-day Saints accept neither the above doctrine of original sin nor the need for Mary's immaculate conception (MD, p. 375). Instead, they "believe that men will be punished for their own sins, and not for Adam's transgression" (A of F 2), because Jesus' Atonement redeems all, including Mary, from the responsibility for Adam's trespass (Moro. 8:8). "God having redeemed man from the fall, men became again, in their infant state, innocent before God" (D&C 93:38). For Latter-day Saints, Mary was a choice servant selected by God to be the mother of Jesus.
"Immaculate Conception." New Catholic Encyclopedia, Vol. 7, pp. 378-82. New York, 1967.
Watlington, Amanda G. Official Catholic Teachings: Christ Our Lord. Wilmington, 1978.