As Corki said, IVF really is the other side of the coin of contraception. Contraception wants sex without babies. IVF wants babies without sex. Both acts divorce sex and babies from their natural context and their natural ends.
EDIT: Here is how the Catechism of the Catholic Church explains it:
2376 Techniques that entail the dissociation of husband and wife, by the intrusion of a person other than the couple (donation of sperm or ovum, surrogate uterus), are gravely immoral. These techniques (heterologous artificial insemination and fertilization) infringe the child’s right to be born of a father and mother known to him and bound to each other by marriage. They betray the spouses’ “right to become a father and a mother only through each other.” 
2377 Techniques involving only the married couple (homologous artificial insemination and fertilization) are perhaps less reprehensible, yet remain morally unacceptable. They dissociate the sexual act from the procreative act. The act which brings the child into existence is no longer an act by which two persons give themselves to one another, but one that “entrusts the life and identity of the embryo into the power of doctors and biologists and establishes the domination of technology over the origin and destiny of the human person. Such a relationship of domination is in itself contrary to the dignity and equality that must be common to parents and children.”  “Under the moral aspect procreation is deprived of its proper perfection when it is not willed as the fruit of the conjugal act, that is to say, of the specific act of the spouses’ union . . . . Only respect for the link between the meanings of the conjugal act and respect for the unity of the human being make possible procreation in conformity with the dignity of the person.” 
 CDF, Donum vitae II,1.
 CDF, Donum vitae II,5.
 CDF, Donum vitae II,4.