If I understand the code right, sims cannot get pregnant if they are abducted from a community lot. (I may have changed this in one of my hacks, but I can't remember if I decided to do that or not, now.) IIRC, this only applies to the dance sphere since (unless you have Inge's default replacements) telescopes cannot be placed on community lots at all. It might be possible to get pregnant from community lot abduction via telescope if you have Inge's telescopes, though. I haven't tried it.
Are you referring specifically to alien abduction pregnancies here? In a vanilla game, sims can get knocked up via public woohoo.
As for alien preggos, I've never had a regular abduction, let alone a dance sphere one...