Is it obligatory to make up prayers after a miscarriage in the third month for a fetus that had no heartbeat or growth, and can all obligatory prayers be made up at once or separately?

If the miscarriage does not show human formation, then the bleeding is considered irregular bleeding (istihada), except for what coincides with the period of menstruation, which is then counted as menses (hayd).

If human formation is evident in the miscarriage, then the bleeding is considered postpartum bleeding (nifas), and ghusl (ritual bath) becomes obligatory after it ceases. It is not permissible to delay ghusl and abandon prayer for forty days if the bleeding stops before that.

Therefore, one must calculate and make up the prayers that were missed and were obligatory to perform, as they are a debt upon one's conscience.