Cursed Womb

A Curse Womb (呪胎) refers to the uterus-like apparition within which a Cursed Spirit grows.

Description
Curse Wombs that grow and change shape are expected to produce Special Grade Cursed Spirits. A Curse Womb can be created from a powerful Cursed Object such as one of Sukuna's fingers. It attracts other Curses in the area and after gathering enough Cursed Energy, the Curse Womb gives birth to a Special Grade Curse imbued with the strength of the Cursed Object used to create it.

Death Painting Womb
A Death Painting Womb (呪胎九相図) is a type of Curse Womb that is half-human, half Cursed Spirit. It is unclear how they are formed precisely. In the Meiji era, the Jujutsu Sorcerer Noritoshi Kamo experimented on the nine aborted fetuses from a girl who could give birth to children who were half Curse. The first three—Choso, Eso, and Kechizu—were strong enough to become Special Grade Curses.

Trivia

 * Kusōzu (九相図) is a Buddhist series of nine paintings that depict the stages of death and decomposition of a corpse.