It is a good when a new person comes into existence; God still creates a rational soul out of nothing even for those conceived as a result of sin.
But it is never moral to use evil means
- in the case of IVF:
- depriving a child of his or her right to be conceived in an act of marital love
- masturbation to obtain semen
- killing many people by subjecting them to harsh living conditions (Petri dish) when their proper place for their age is in a woman's womb
A high fraction of those conceived with IVF do not survive because of the harsh living conditions, so many ova have to be fertilized for there to be a chance of one surviving long enough to be implanted in the woman's womb.
to achieve a good end:
- bringing a new life into existence.
The authoritative Magisterial source on IVF is Donum Vitae, a 1987 document from the CDF. It says that even if masturbation and grave danger to the life of the embryo could be avoided, IVF is still intrinsically immoral because it deprives the child of his God-given right to be procreated in an act of marital love. Look at section A.1, “Why must human procreation take place in a marriage?”
For more information on this, see the discussion on IVF in Health Care Ethics: A Theological Analysis by Benedict Ashley, O.P.
("Artificial Human Reproduction" on p. 86 of the PDF or §9.2 "Reproductive Technologies" of the EPUB)
There are moral, more successful alternatives to IVF, such as Dr. Hilger's NaProTECHNOLOGY. You can find a NaPro doctor here. See also The NaProTechnology Revolution: Unleashing the Power in a Woman's Cycle and associated website.