1) THE "TUM'AH" OF A "ME'UBERES"
QUESTION: The Beraisa lists the various types of women who are Metamei me'Es l'Es when they see Dam. Included in the list is a Me'uberes (a pregnant woman).
This Beraisa seems to contradict the Mishnah earlier (7a) which says that the more lenient ruling of Dayah Sha'atah applies to a Me'uberes! What is status of a Me'uberes who sees Dam?
ANSWERS:
(a) TOSFOS (DH veha'Yoledes) answers that the Mishnah earlier is discussing blood that a woman sees during the normal course of her pregnancy, and that was not caused by birth pangs. Blood that comes as a result of birth pangs is different; the law is stringent for such blood, and she is Metamei me'Es l'Es. The RITVA explains that since it is the birth that causes the flow of blood, and we do not know exactly when the effects of birth started to cause this flow of blood, it makes sense to rule that she is Metamei me'Es l'Es.
The MAHARI SHAPIRA explains this further. The Gemara in Shabbos (129a) records a dispute about when exactly a woman becomes a Nidah when she is giving birth. Abaye says that she becomes a Nidah when she crouches on the birthing stone. Rav Huna says that she becomes a Nidah when the blood starts flowing. The dispute appears to be due to the fact that we do not know exactly when the "Pesichas ha'Kever" -- which makes a woman Tamei (as the Gemara says, "Ein Pesichas ha'Kever b'Lo Dam") -- occurs during the birthing process. Since it is unclear when the Pesichas ha'Kever occurs, it is logical to rule that a Me'uberes who sees blood while in labor is Metamei me'Es l'Es.
(b) Alternatively, Tosfos answers that the Beraisa is following the opinion of Rebbi Yosi who maintains that a Me'uberes is given the status of Dayah Sha'atah only when three Onos passed and she saw no blood. The Beraisa is discussing a case in which three Onos did not yet pass.
(c) Tosfos suggests a third explanation. The Gemara earlier (10b) records a dispute about the intent of the Mishnah there (7a) which says that a Me'uberes has the lenient ruling of Dayah Sha'atah. Some maintain that the Mishnah gives the status of Dayah Sha'atah to a Me'uberes only on the first occasion that she sees blood. When she sees blood on subsequent occasions, the Halachah is that she is Metamei me'Es l'Es. Tosfos explains that according to that opinion, the Beraisa here may be referring to the second time she sees blood during her pregnancy. The new teaching of the Beraisa -- which we would not have known from the Mishnah alone -- is that even when the second flow of blood is due to labor and not Dam Nidah, the woman is still Metamei me'Es l'Es. (Y. MONTROSE)
2) ESTABLISHING A "VESES" DURING "YEMEI ZIVAH"
QUESTION: The Gemara quotes Shmuel who says that blood seen during the days of Zivah does not contribute towards establishing a fixed Veses. RASHI (DH b'Soch) gives an example of a woman who saw blood once, and then she saw blood two more times at fifteen-day intervals.
If the woman saw blood fifteen days after seeing blood during the days of Zivah but did not see blood in the interim, then how can the second show of blood also occur during the days of Zivah? The days of Zivah last for only eleven days if a woman does not see blood; once those eleven days pass, the next show of blood makes her a Nidah and not a Zavah!
ANSWERS:
(a) The RAMBAM (Hilchos Isurei Bi'ah 6:4-5) rules that a woman's cycle is a constant cycle of seven days of Nidah followed by eleven days of Zivah. Even if she does not see blood after her days of Zivah pass, she still begins to count seven days of Nidah, during which any blood she sees is considered Dam Nidah. Accordingly, it is clear how two different shows of blood can be fifteen days apart and still both be during days of Zivah, even if the woman did not bleed in the interim.
(b) The MAHARSHA and MAHARAM suggest that Rashi does not mean that all of the Re'iyos occurred during the days of Zivah. Rather, Rashi means that all of the appearances of blood that occurred during the days of Zivah do not join to create a Veses. The woman, however, certainly must have seen blood during Yemei Nidah as well (in order to begin a new cycle of days of Zivah before the appearance of blood on the fifteenth day).
(c) The ARUCH LA'NER suggests (based on Rashi to 11a, DH Gemara) that the Gemara means that if the third appearance of blood occurs during the days of Zivah, it cannot join the two previous appearances of blood to create a Veses. (However, as the Aruch la'Ner points out, this is not in agreement with the words of Rashi here.)

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3) A "VESES KAVU'A" TOGETHER WITH A "VESES SHE'EINO KAVU'A"
QUESTION: Rebbi Yochanan rules that when a woman sees blood on Rosh Chodesh, on the following Rosh Chodesh, on the twenty-fifth day of the month, and again on Rosh Chodesh, her Veses Kavu'a is established to occur on Rosh Chodesh. The TUR (YD 189) rules that she also must observe a Veses she'Eino Kavu'a on the twenty-fifth day of the month.
The CHAVOS DA'AS (#15) asks that there is a rule that once a woman has a Veses Kavu'a, she does not have to be concerned for any Veses she'Eino Kavu'a. In the case of Rebbi Yochanan, since this woman has established a Veses Kavu'a of Rosh Chodesh, why does she need to be concerned for a Veses she'Eino Kavu'a of the twenty-fifth day of the month?
ANSWER: The CHAVOS DA'AS explains that there is a difference between a Veses of Haflagah (intervals) and a Veses ha'Chodesh (of fixed dates). A woman who has a Veses of seeing blood at fixed intervals need not be concerned for any Veses she'Eino Kavu'a of other intervals, because her intervals are fixed. However, when a woman has a Veses of seeing blood on fixed dates (but not regular intervals), this indicates that there are certain external factors that are influencing her Veses. One factor is not necessarily exclusive of another, and therefore she must be concerned for both Rosh Chodesh and the twenty-fifth day of the month.

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