What is the ruling on very little, intermittent brown discharge that precedes menstruation, and is it considered menstruation that prevents one from performing Umrah?

The maximum duration of menstruation is fifteen days, and the minimum is one day and one night. The minimum duration of purity (between menstruations) is fifteen days. If bleeding continues for one day and one night or more, and does not exceed fifteen days, and it is separated from another bleeding period by a period of purity lasting fifteen days, then both are considered independent menstruations. However, if the bleeding continues for more than fifteen days, or if it is less than that and is not separated from the next bleeding by a fifteen-day period of purity, then not all of it is menstruation:

If you have a regular monthly habit, you should refer to your accustomed days, and the remainder is blood of istihadah (irregular bleeding). If you do not have a habit, you should differentiate between menstrual blood and istihadah blood. If you are unable to differentiate, you should consider yourself to be menstruating for the usual duration of menstruation (six or seven days) after investigation, and then perform ghusl (ritual purification).

During Umrah, one must cease circumambulating (Tawaf) and entering the mosque upon the onset of menstruation. However, ihram (ritual consecration), sa'i (the ritual walk between Safa and Marwah), and shaving/cutting hair are not prevented by menstruation. If menstruation begins before or during Tawaf, one must stop until purity. But if it begins after Tawaf, you may complete Sa'i and shaving/cutting hair.