What is the ruling on secretions mixed with light red blood before menstruation, and blood that exits only during urination or defecation at the beginning and end of menstruation and after purification, and is this considered menses or istihadah (irregular bleeding)? What is the most cautious approach regarding prayer and ghusl in these cases?

Every blood a woman sees during the period of possibility is considered menstruation. The minimum for it, according to the majority of scholars, is one day and one night. Therefore, ghusl (ritual purification bath) is not required for the discharge you see before menstruation that stops, unless it reaches one day and one night. As for the Maliki school, the minimum for menstruation is a single discharge, and it is more prudent to perform ghusl after any blood drops at the beginning of menstruation cease. If the blood stops immediately after being seen, ghusl is not required of you according to the majority of scholars if the cessation occurs before one day and one night. Any returning blood you see after seeing purity is considered menstruation as long as it is within the period of possibility, and ghusl is required after it stops, even if it is just drops. Some scholars are of the opinion that a short intervening period of purity is not considered, and this is the choice of Ibn Qudamah and Ibn Uthaymeen, and there is no harm in acting upon it. As for yellowish or brownish discharge after the blood has stopped, it is not to be given attention.