Several years back, I had a sim that was abducted 6 times. Only two resulted in pregnancies though. He later married an alien and had a baby with her. Their daughter was just a normal sim with green skin.
Recently, in my alien legacy (different family, different save), my founder, who is an alien was abducted twice but only got pregnant once. His oldest daughter, who was another normal sim with green skin, got abducted and got pregnant. She was abducted for a second time but she didn't get pregnant that time.