Under what category falls the bleeding after an abortion?

This question made me ask myself: After an abortion (miscarriage) or an artificial (or induced) abortion a woman usually sees some blood for a couple of days. As what kind of blood is this bleeding qualified by scholars: as menses حيض (I would exclude this option), childbed bleeding نفاس (nifaas) or as a vaginal bleeding (not menstruation) استحضة (istihaadah)?