The date of the menses is established by three consecutive times. That is, if menstruation began three consecutive times, at a similar time, then this date is her established date of the menses. There are women who establish their periodic menses at certain days of the month. For instance, if she perceived the flow three consecutive times, each time on Rosh Chodesh (New Moon), then her established menses is on Rosh Chodesh. Also if she perceived it three consecutive times on the fifth of the Jewish-Hebrew month, then the fifth day of the Jewish-Hebrew month is the established day of her menses. This way of reckoning is referred to as "Menses determined by days," for it is consistently the same day in the month. And even though the number of days between one perception and the other is not always alike, for some months consist of only twenty-nine days, while others consist of thirty days, nevertheless, since she is accustomed to perceive on a certain day of the month, this day is her established day of the menses.

Most women, however, are accustomed to establish a mensal pattern of "equal intervals", which is a separation from one perception to another of an equal number of intervening days. For instance, if she perceives a flow and twenty-five days elapse, or thirty days or thirty-two days or the like, and following she again perceives a flow. If she had these perceptions on three consecutive equal¹ 85:34. intervals, this is her established date of the menses, and is referred to as the menses of "equal intervals." And after another interruption of that number of days, the following day is her established date of the menses. Since the menses cannot be established by less than three times, and an interval cannot be recognized by less than two perceptions; therefore, establishment of the menses of equal intervals requires four perceptions. For instance, if she perceived a flow today, followed by an interval of twenty-five days, and she perceived, followed again by an interval of twenty-five days, and she perceived, followed again by an interval of twenty-five days, and she perceived, she has had four perceptions, between which there were three equal intervals, and has thereby established her menses.

footnotes: ¹ If this sequence had been interrupted by a flow after a shorter interval elapsed, this does not upset the establishment of the longer interval. For example, if she perceived after twenty days on two consecutive occasions, and then perceived after a fifteen day interval, and then again after a twenty day interval, she has thus established a twenty day cycle. But if, instead of the fifteenth, she had seen on the twenty-fifth, she has not established her menses. Chazon Ish

There are some women who do not have an established date of perception, neither of the days of the month, nor of equal intervals, but do experience various physical symptoms.² For instance, it is charactaristic of her to yawn before menstruation, in the manner of one who stretches his arms from weariness, or like a person who opens his mouth (yawns) from drowsiness, or like a person who burps because of the food he has eaten—all of these are included in "yawning." Similarly, if she flatuates or sneezes, or feels some pain in the region of the navel or the womb, or she has an attack of chills and fever, or the hair of her body bristles, or her head and (her) limbs grow heavy. If she experienced any of these symptoms, on three consecutive periods, and immediately began menstruation, this symptom serves as her established date of menses. And this is referred to as "Menses regulated by physical symptoms."³ 189:19. At that time she must examine herself to see if she is menstrually clean. Eshkol 34. If she did not examine herself, she remains forbidden until she does and finds herself menstrually clean. See Shulchan Aruch 184:9. Yawning and sneezing only when repeated many times consecutively are regarded as symptoms by which to establish a date of menses, but if she yawns or sneezes one time, the date of menses is not established for it is a natural and normal thing. The date of menses is established by symptoms only if she perceived each of the three times through one particular symptom. But if once it occurs through one symptom and once through another symptom, it is not considered established.

footnotes: ² That are brought on by the oncoming menses. ³ During the onset (day or night) when she experiences one of these symptoms, she is forbidden to you. Shulchan Aruch

Some women establish their menstrual periods by monthly, or by equal intervals, combined with yawning, sneezing, or similar physical symptoms. For instance, every fifth day of the month she yawns or sneezes, and then perceives the flow, or when twenty-five days from perception elapse, she yawns or sneezes, and then perceives the flow. This is referred to as "menses regulated by combining factors." That is, it is a combination of a regular date and a physical symptom. If this pattern occurs three (consecutive) times, then, when that regular day arrives, and she yawns or sneezes, she must be concerned about her perception. But with the arrival of that day alone, or with yawning and sneezing alone, she need not be concerned, since she has regulated her term only with the two factors combined.

A woman whose periods are regular, is at all other times presumed to be menstrually clean, and her husband may have marital relations with her, and does not have to inquire about her status. Even if she is partly asleep he may have marital relations with her, and she does not need to examine herself, either before marital relations or afterwards. On the contrary, she should not examine herself in the presence of her husband,⁴ so that he will not be apprehensive, thinking she probably felt something, for if she did not feel something she would not have examined herself. Therefore if she examines herself in his presence, before having marital relations, there is cause for concern, that perhaps because of his apprehension he might keep away from her.⁵ 186) And if she examines herself in his presence after having marital relations, there is cause for concern that perhaps he will be apprehensive, thinking that she probably felt something while having marital relations, and will keep away from her the next time. Therefore, she should not examine herself in her husband's presence. But if not in her husband's presence, the more a woman examines herself, the more praiseworthy she is.

footnotes: ⁴ Not necessarily his presence but rather his knowledge. ⁵ And thus neglect the mitzvah of propagation. (L’vush

A woman whose periods are totally irregular should examine herself before and after having marital relations. The husband, too, should wipe himself⁶, but the Rosh maintains this is unnecessary; and this is the accepted custom. after marital relation's to ascertain whether there is a drop of blood. However, if her flow of blood is assumed to have ceased, for instance, a pregnant woman after the first three months of pregnancy, or one who nurses, or a woman who is old, these need not examine themselves.

footnotes: ⁶ Rambam

There are women who do not have a regular cycle, but have, nevertheless, a certain number of days during which they do not perceive any flow. For instance, a woman who has ascertained that during the twenty-five days after her perception of a flow, she does not perceive another flow, but only after that, and then she has no definite date, because sometimes she delays one day, or two or three days. Since it has been established three times, that during these days she does not perceive, a woman until twenty-five days elapse, is regarded during these days like a woman who has a regular menstrual cycle. But on the days that follow when she is uncertain, and cannot be presumed to be menstrually clean, she is forbidden to her husband.