What is the ruling regarding the four days that the wife broke her fast, assuming it was menstrual blood, and then it became clear that it was abnormal bleeding (istihadha)? And is expiation (kaffarah) due upon her? If so, what is it?

If the days of bleeding increase due to the IUD, and the blood is continuous, then all of it is menses. However, if the bleeding stops after the usual period, and then returns, differing from the well-known menstrual blood due to the IUD, then it is istihadah (non-menstrual vaginal bleeding). Likewise, if medicine clarifies that it is bleeding from a hemorrhage and not menses.

If a woman breaks her fast, believing it to be menstruation, and then it becomes clear that it was istihadah, she is only required to make up the days she missed fasting.