During prayers...
During prayers: If a woman feels while praying that the intensity of the blood flow changed from less to more: If by discontinuing the prayers there is no fear that they will become Qadha, then a woman should discontinue praying and take care of the duty as per the rules, then perform prayers. Further explanation: If a woman starts praying and realizes that the blood flow has increased then she should see if there is enough time left so that her prayers do not get Qadha.
If there is enough time left then she should discontinue her prayers. After discontinuing her prayers she should check to see if the flow has increased to medium or excessive istihadha, and then follow the rules accordingly. If there is not enough time left, then she should not discontinue the prayers. She should complete the prayers, then check to see if the intensity of the flow increased to medium flow or excessive flow.
Follow the rules accordingly, and then repeat the prayer again with the intention of Qadha. Change of Flow from More to Less Katheera to Qaleelah (Excessive to Little) Katheera to Mutawassitah (Excessive to Medium) Mutawassitah to Qaleelah (Medium to Little) Rules to be followed if the blood flow changes from more to less as stated above: For the first prayer a woman should follow the rules as per the state she was in. Prayers after that are going to be according to the state she is in.
Further explanation: If a woman is in the state of Katheera (Excessive flow) and before praying Dhuhr she realizes that she is in the state of Qaleelah (Little) now, she should follow the rules for Katheera for praying Dhuhr and then for Asr she should follow the rules for Qaleela.
If a woman after Dhuhr realizes that state she is not in a state of Katheera anymore but she is in a state of Qaleela now, she should still follow the rules for Katheera for praying Asr and then for Maghrib and the prayers after that she should follow the rules of Qaleela. Fasting during Istihadha During Qaleela: A woman should follow the rules she follows before prayers. With the only exception that a cotton should be inserted inside the vagina to prevent the blood from gushing out.
(As per Imam Khomeini this is Ihtiyat-e-Wajib for all the states of istihadha) During Mutawassitah: A woman should follow the rules she follows before prayers. With the only exception that a cotton should be inserted inside the vagina to prevent the blood from gushing out.