http://www.catholicinsight.com/online/church/vatican/article_475.shtml

A human being comes into existence at the moment of fertilization of an oocyte (ovum) by a sperm. This fact has been recognized by the science of Human Embryology since 1883, and is still acknowledged today. The Church teaches that a human being must be respected – as a person – from the very first instant of his existence as a human being, and therefore, from that same moment, his rights as a person must be recognized among which in the first place, is the inviolable right of every innocent human being to life. The Church also teaches that from the moral point of view a truly responsible procreation vis-à-vis the unborn child, must be the fruit of marriage.

Pope Paul VI has taught that there is an “inseparable connection, willed by God, and unable to be broken by man on his own initiative, between the two meanings of the conjugal act: the unitive meaning and the procreative meaning.”

IVF violates the rights of the child: it deprives him of his filial relationship with his parental origins and can hinder the maturing of his personality. It objectively deprives conjugal fruitfulness of its unity and integrity, it brings about and manifests a rupture between genetic parenthood, gestational parenthood, and responsibility for upbringing. This threat to the unity and stability of the family is a source of dissension, disorder, and injustice in the whole of social life.

What about research on a human embryo?
The Church teaches that medical research must refrain from operations on live embryos, unless there is moral certainty of not causing harm to the life or integrity of the unborn child and mother, and on condition that the parents have given free and informed consent to the procedure. Since stem cell research on human embryos, in practice, invariably causes the death of those embryos, it too stands condemned.

In summary, the Catholic Church condemns as gravely evil acts, both IVF in and of itself, and stem cell research performed on IVF embryos.

References:

1. Donum vitae (Respect for Human Life), Instruction on respect for human life in its origin, Congregation for the Doctrine of the Faith, 1987. (Available from Catholic Insight under the title “Vatican, High Tech”). Note: see also “Moratorium” in News in Brief, under Great Britain, p. ????

2. Encyclical letter Humanae vitae, No. 14, AAS 60 (1968), 488-489.

3. Donum vitae.