Nicene and Post-Nicene Fathers, Vol. III:
Moral Treatises of St. Augustin: Section 10

10. For not even herein ought such as are married to compare themselves with the deserts of the continent, in that of them virgins are born: for this is not a good of marriage, but of nature: which was so ordered of God, as that of every sexual intercourse whatever of the two sexes of human kind, whether in due order and honest, or base and unlawful, there is born no female save a virgin, yet is none born a sacred virgin: so it is brought to pass that a virgin is born even of fornication, but a sacred virgin not even of marriage.