Purity: Nifas After Miscarriage
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 499:
It is not necessary for the baby to be fully developed; even if it is born under-developed, as long as its development has passed the stage of an ʿalaqah, which is a clot of blood, and a muḍghah, which is a lump of flesh [embryo], and it is miscarried, then the bleeding of the woman for ten days is considered to be nifās.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)