What does the Catholic church teach about IVF?

I met a Catholic family two years ago that utilizes in vitro fertilisation (IVF). I am inclined to believe that IVF is a completely moral practice in situations where a couple may be infertile. I think this particular couple told me that they use IVF not because of infertility issues, but because they have a right risk of conceiving children with mental disabilities. I don't remember the exact details, but I think they said that multiple eggs are fertilized and whichever one presents the least genetic risk of retardation is implanted in the mother's uterus. If this wasn't the case, then they may have said that another woman donates her eggs for IVF. The first alternative sounds a lot like abortion to me, and thus would be a mortal sin. The second alternative does not seem as bad, but it still feels morally questionable. This leaves us with three different IVF procedures: 1. A single egg is fertilized from the mother due to infertility. 2. Multiple eggs are fertilized from the mother and the "best candidate" is kept. 3. A different woman donates eggs for fertilization. Even if I am misremembering the circumstances from my anecdote, I believe these to all be real IVF procedures used in the world today. What is the Catholic Church's guidance on these procedures?