Why is a three-month waiting period required after the initial nine months for a woman whose menses have ceased, given that the womb is considered outwardly pure after nine months?

Primary text

The requirement of three additional months after the initial nine months when menstruation ceases without cause is because the waiting period based on menstrual cycles or months is only established in the absence of pregnancy. The waiting period remains obligatory even when the womb's purity is known, as evidenced by the ruling that if a divorce is contingent upon giving birth, the divorce occurs and the waiting period becomes binding upon the laying down of the child, even if purity was previously known. The purpose of the waiting period is establishing purity, which is achieved within the nine months, but the established procedure requires adherence. Furthermore, prolonging the waiting period causes harm, as it prevents her from remarrying and keeps her perpetually confined, and it imposes costs of residence and maintenance upon the husband.