2,128. More Human-Like and Non-Human-Like Forms

Hilchos Issurei Biah 10:10

If a woman miscarries and expels something snake-like, she is rendered unclean from birth impurity because the eyes are round like those of a human. If she expels a fetus that has a human shape but also wings of flesh, she is unclean from birth impurity. If a fetus has one eye and one thigh on the side, it is considered half a human being and the mother is unclean from birth impurity; if they’re in the middle, she remains ritually clean because this isn’t a human-like form.

Hilchos Issurei Biah 10:11

If a fetus’ trachea is closed or its body is missing from the umbilicus down, but rather is a mass of flesh, or its skull is just a mass of flesh, or its face was shapeless so that its features are unrecognizable, or if it has two backs and two spines, or if the shape of the head or the hand are not defined – in all of these cases, the mother is not rendered unclean from birth impurity. If she expelled a severed hand or foot, we presume that it came from a whole fetus and it counts toward the greater number of limbs (to impart ritual impurity).