The Church is kind of traditional when it comes to creating life, as I'm sure you have noticed. It even opposes non-marital heterosexual activity to create life, so this has nothing to do with a certain favorite issue of the Left.
Once a life has been created, though (regardless of how) it must be protected like any other life.
So, you are talking about 2 issues, life creation and life sustainment.
Just for example, some infertility treatments (and surrogacy processes) result in many deaths to select one life, so such "treatments" are opposed because they involve killing humans. Again, nothing to do with gays, and everything to do with life creation, and then sustainment, morality.
Others can explain it better than I can. It gets quite theological on the creation side. The sustainment side is easy though: don't kill.