1,074. Other Types of Menstrual Patterns
154:2 Most women establish the start of their periods by regular intervals. That is to say, the interval between first seeing blood is the same from month to month. For example, if she sees blood once and then there is a break of 25 days, 30 days or 32 days, she waits to see when it comes again. If she sees three regular intervals in a row, she has established a pattern. This is called "veses haflagos" - a menstrual pattern based on intervals. After this interval of days has gone by, the next day is considered the start of her period. Since a pattern cannot be established with fewer than three times, and an interval can only be set by seeing blood twice, in order to establish her menstrual pattern she must see blood four times. For example, if she saw blood today and there was a 25-day interval until she saw blood again, then another 25-day interval and she saw blood again, then a third 25-day interval and she saw blood again, all together she saw blood four times with three regular intervals in between. This establishes the start of her period.
154:3 There are women who don't have a fixed day for the start of their periods, neither a day of the month nor a regular interval. Instead, they have bodily symptoms. For example, before her period arrives, she is accustomed to yawn or hiccup, pass wind or belch, or she feels pain in her stomach or uterus, or she feels feverish or her body hair stands up, or her head or limbs feel heavy. If any of these things happened three times in a row and afterwards saw blood, this establishes the start of her period. This is called "veses haguf" - a menstrual pattern of the body. Only yawning or hiccuping, etc. several times in succession can be a sign of the start of a period; belching or sneezing just once cannot establish a pattern because this is a normal thing for people to do. Similarly, we only establish a pattern if she has the same symptom three times; if one time there was one symptom and the next time another symptom, it does not establish a pattern.