Some Bible interpreters regard Genesis as suggesting that angels had sex with earthly women:
"The sons of God saw the daughters of men, that they were fair; and they took them wives of all which they chose" (Gen.6:2). 
This interpretation assumes that "sons of God" refers to angels, while "daughters of men" refers to human females.
The Unification Church cites Jude 1:6-7 as evidence that angels "sinned" via "fornication":
- And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day.
- Even as Sodom and Gomorrha, and the cities about them in like manner, giving themselves over to fornication, and going after strange flesh, are set forth for an example, suffering the vengeance of eternal fire. (King James Version)
These views are considered unorthodox within mainstream Christian thought. The points at issue are:
- Can angels sin? Have any angels ever sinned?
- How can an angel have sexual congress with an earthly woman?
- Would this relationship result in pregnancy?
- Does this have anything to do with the fall of man?