Whoever touches a dead body, the body of a human being who dies, and does not purify himself, defiles the Mishkan of the Lord, and that person shall be cut off from Yisrael; because the water of sprinkling was not thrown upon him, he shall be unclean; his uncleanness is still upon him.
Torah Temimah: Chullin 72a — Rabbi Akiva says: A fetus in a woman’s womb is unclean, for the verse says “whoever touches a dead body in the soul of a human”; what is a dead body that is in the soul of a human? You must say this is a fetus in a woman’s womb.
English: Rabbi Akiva says: A fetus in a woman’s womb is unclean, for the verse says “whoever touches a dead body in the soul of a human”; what is a dead body that is in the soul of a human? You must say this is a fetus in a woman’s womb.
Identification of “dead body in the soul of a human” as a fetus.
A fetus that dies in the womb is itself a source of corpse impurity.