Gemara

(Rav Yosef): If the time for the Chupah came and she became a Nidah, he need not feed her.

56a Question (Rav Ashi): If she entered Chupah and became Nidah, what is the law?

If Chivas (the dearness of) Chupah acquires, this is only a Chupah fitting for Bi'ah;

Or, perhaps we do not distinguish!

The question is unsettled.

Yevamos 57 (Rav): Yesh Chupah l'Pesulos (Chupah takes effect even if she is forbidden to him).

(Shmuel): Ein Chupah l'Pesulos (it does not take effect).

(Shmuel): If a girl is under three years and a day, Rav agrees that since Bi'ah with her is not considered Bi'ah, Chupah does not take effect on her.

(Rav Amram citing Rav Sheshes) Yesh Chupah l'Pesulos. A Mishnah supports this.

(Mishnah): (A Sotah answers) "Amen" that she was not Mezaneh when Mekudeshes, Nesu'ah, Shomeres Yavam (when awaiting Yibum), or after Yibum.

We cannot say that he warned her and took her to drink during Eirusin, for an Arusah does not drink;

If he warned her and she was secluded during Eirusin, and he took her to drink after Nisu'in, the water would not test her (for Nisu'in was forbidden after seclusion)! "The man will be clean from sin" - the water tests her only if he is clean from sin!

Rather, he warned her and she was secluded during Eirusin, and he had Chupah without Bi'ah. This teaches that Chupah takes effect on Pesulos.

Rishonim

Rif (Kesuvos 22b): Rav Ashi's question was not answered. Therefore, Chupas Nidah does not acquire.

Rambam (Hilchos Terumos 7:21): If a divorced Kohenes entered Chupah with a Kohen, without Eirusin, this disqualifies her from eating Terumah.

Kesef Mishneh: This is like Rav.

Rambam (Hilchos Ishus 10:2): Once an Arusah enters the Chupah, her husband may have Bi'ah with her at any time and she is his full wife in every respect. She is called Nesu'ah even before Bi'ah, as long as Bi'ah was permitted. If she was Nidah, even if she entered the Chupah and was secluded with him, Nisu'in was not finished and she is still an Arusah.

Magid Mishneh: The Gemara asked whether or not Chupas Nidah acquires regarding (Tosefes) Kesuvah. The Rif says that since the question was not answered, it does not acquire. The Rambam and some Ge'onim explain that it does not acquire for anything, e.g. inheritance or Tum'ah. Some say that the question was only about Kesuvah, but it acquires for everything else.

Question (R. Akiva Eiger): The Magid Mishneh connotes that the Rambam agrees that Chupas Nidah does not acquire because it is a Safek. This is difficult. 'She is still an Arusah' connotes that she is a Vadai Arusah, and her father can receive her Get, and if she was widowed her Kesuvah from a future husband is 200, and her brother (a Kohen) is Metamei for her!

Rebuttal (of Rambam - ha'Ramach): We find that when Rav traveled he would have Chupah with a woman (Yevamos 37b). Even though Bi'ah was forbidden for seven days (lest her desire caused a discharge of blood), the Chupah would permit her afterwards without need for another Chupah!

Question (Ran DH u'Pirsah): The Rif did not specify. It seems that he holds like the Rambam, who says that Chupas Nidah does not acquire at all. This is difficult. We hold that Yesh Chupah l'Pesulos (Yevamos 57b)! Rather, the question was only about Tosefes.

Answer #1 (Lechem Mishneh): Yesh Chupah l'Pesulos when he intends to have Bi'ah in spite of the Isur. In Yevamos; he marries a woman permanently forbidden to him, intending to have Bi'ah with her b'Isur. In Kesuvos we discuss one who will not transgress. A support for this is the Ri (brought below in Hagahos Ashri), who says that Chupas Nidah acquires if he was aware that she is Nidah.

Question (Lechem Mishneh DH Aval): Here the Rambam explains like Tosfos, that the Gemara (Yevamos 57b) discusses Chupah after Kidushin. In Hilchos Terumos, he explains like Rashi that it discusses Chupah without prior Kidushin, according to Rav Huna who says that Chupah itself makes Kidushin! In Perek 3 of Ishus, the Rambam does not say that Chupah makes Kidushin!

Answer (and Answer #2 to Question (iv) - Lechem Mishneh): The Rambam did not want to say that Rav and Shmuel are unlike the Halachah. Therefore, he explains that even though Chupah by itself does not acquire, it can forbid. We find that Zikah to Yibum can forbid to eat Terumah, even though it never permits.

Rosh (Kesuvos 5:6): We hold that the beginning of Chupah acquires, for the end of Chupah is the beginning of Bi'ah. Therefore, if she became Nidah after Chupah began, he already acquired her. The Rambam forbids Nisu'in and Birkos Nisu'in until she becomes Tehorah. He learns from Kesuvos 2a. If she became Nidah (at the time fixed for Chupah) he need not feed her, i.e. because Chupah cannot be done. This is not a proof. Rather, he can say that Chupah is for the sake of Bi'ah, so he will wait until Bi'ah is permitted. Some bring a proof from Nidah 66a, in which Ravina required his daughter-in-law to wait seven days after she agreed to Chupah, for she is Safek Nidah (perhaps her desire caused a discharge of blood). Also this is not a proof. He wanted to wait until the Bi'ah will be permitted! In all places we make Birkas Chasanim even if she is Nidah. However, they may not be secluded, and he must sleep among men and she among women (until she is Tehorah).

Hagahos Ashri: The Ri says that Rav Ashi's question was only when the Chasan thought that she is Tehorah and found out that she is Nidah. Had he known, perhaps he would have delayed the Chupah. It is clear from Kesuvos 2a that the custom was not to have Chupas Nidah. If he was informed and knowingly had Chupas Nidah, he acquires her totally. The Chupah permits Bi'ah when she will be Tehorah. It is proper to inform the Chasan in advance.

Ran (Kesuvos 1a DH Oh): Some say that Chupah is seclusion, and therefore he need not feed her if she became Nidah (at the time fixed for Chupah), for seclusion is forbidden. The Ba'al ha'Itur and the Rambam require that she have a Kesuvah before Chupah, so Bi'ah will be permitted. This is unreasonable. R. Ami permitted first Bi'ah on Shabbos even though she had no Kesuvah (7a); surely, the Chupah was on Wednesday, like Chachamim enacted. We do not find an Isur to be secluded without a Kesuvah, because the Isur of Bi'ah without a Kesuvah is only mid'Rabanan. Also, she will not agree to Bi'ah, for she knows that it is light in his eyes to divorce her. This is unlike when she is Nidah. However, if Chupah is seclusion, a Nidah is not fit for Chupah. B'Di'eved it acquires, for Yesh Chupah l'Pesulos. Others say that Chupah is being in his house, even without seclusion - "V'Im Beis Ishah Nadarah". A proof is from Kesuvos 12a. It says that if a widow from Nisu'in remarries, her next Kesuvah is 100, even if there are witnesses that she was never secluded with her first husband. Even though Chupah can be done with a Nidah, he need not feed her because Chachamim did not obligate him to have Chupah until Bi'ah is permitted. Nowadays we have Chupah without seclusion, so we are not concerned if she is Nidah. Nevertheless it is proper to delay Nisu'in until she is Tehorah. This was the custom. It seems that the custom was also to write the Kesuvah before Chupah. This is why R. Ami did not ask about it.

Poskim

Shulchan Aruch (EH 61:1): Once a man enters his Arusah to Chupah, even if they did not have Bi'ah, she is his full wife in every respect. She collects the Ikar Kesuvah and the Tosefes if she is widowed or divorced. This is if Bi'ah was permitted. If she was Nidah and then entered the Chupah and was secluded with him, she is not his (Nesu'ah) wife. She is still an Arusah.

Beis Yosef (DH u'Mah she'Chosav ba'Meh): Rav Ashi's question was not settled. It is a Safek if she gets Tosefes, so we do not take from him.

Question (Beis Shmuel 2): The Rambam (Hilchos Ishus 10:1) says that Chupah is seclusion. Since seclusion is forbidden with her if she is Nidah, why was Rav Ashi unsure if Chupas Nidah acquires?

Answer (R. Akiva Eiger 3): The Ran (1a DH Oh) initially said that Chupah is seclusion. Chupas Nidah acquires, even though it is forbidden. The Rambam holds that the conclusion is that it does not acquire, but this was not obvious.

Rema: The Kesuvah must be written before Chupah in order that it will be a Chupah in which Bi'ah was permitted. The opinion that says that Chupas Nidah is Chupah even though Bi'ah was forbidden says the same if there was no Kesuvah.

Chelkas Mechokek (3): One can be lenient even according to the opinion that Chupas Nidah does not acquire.

Rema: Nevertheless, the custom is to write it beforehand. If a woman is deathly sick and he does Chupah in order to inherit her, it is not a Chupah, for she cannot have Bi'ah at all. Chupah is valid even if the Berachos were not said beforehand. L'Chatchilah, they should be said before seclusion.

Shulchan Aruch (2): It is proper not to have Nisu'in until she is Tehorah.

Beis Yosef (DH u'Mah she'Chosav Od): Since he may not have Bi'ah or even be secluded with her until she is Tehorah, it is improper to have Chupah.

Rema: Nowadays the custom is not to wait to be particular about this. Nevertheless, it is proper to inform the Chasan beforehand that she is Nidah.