Now that I think about it, I can't remember Catholics explicitly forbidding oral sex, either, though I can't recall them endorsing it either (unlike vaginal sex during the woman's infertile days), so I'm assuming they aren't technically OK with it. They do clearly forbid IVF (which is one of the zillion reasons why Angels and Demons by Dan Brown is ridiculous), though, since many of them are kind-of sort-of reasonable, I wouldn't expect that to make much of a fuss about semen analyses (given that the pleasure of the orgasm isn't the point, and figuring out whether you haven't had a baby yet because of bad luck or because you're sterile is).