Hi SimmieMaus,
AR is designed as a Maxis Match mod, with the same likelihood of pregnancy (50/50) as in the vanilla unmodded game. In the vanilla game only male sims age YA or older can get pregnant via alien abduction. If a teen female sim was able to get pregnant before you most likely have one or more other mods installed that is enabling that (EA does not allow/enable teen pregnancy in general). The most likely candidate is MCCC and MCCC's MC Occult module, which partially overrides my alien abduction coding.
If you do have MC Occult installed and enabled, it will let you choose if you want female sims to be pollinated and you can manually set the likelihood of pregnancy there. You may need to ask the Deaderpool support server for the rest.
Best,
OneMoreKayaker