Must a woman fast on a regular fast day [Tzom Gedalia, Asara Beteves, 17th Tamuz] if she is within two years of giving birth?

General law by a nursing women:[1] Pregnant and nursing women are exempt from fasting a regular fast day.[2] This applies even if they do not experience pain in fasting, nevertheless, they are not obligated to fast.[3] Nevertheless, the custom of pregnant and nursing women is to be stringent to fast[4], unless they experience great pain [or feel weak[5]] in which case they are not to fast.[6] They are likewise not required to make up the fast at a later date.[7] [Practically, the widespread custom today is that pregnant and nursing women do not fast any of the fasts other than Tisha B’av and Yom Kippur, as they are all considered weak and in pain.[8] They are also not required to make up the fast at a later date.[9]]

The definition of a nursing woman: Some Poskim[10] rule that all women within 24 months after birth [child is less than 2 years old] are defined as nursing women, even if they are not actually nursing anymore.[11] Other Poskim[12] however are stringent to require any woman who is not actually nursing, to fast. Practically, one is to be stringent in this matter, unless she is not feeling well, or is pregnant, in which case one may be lenient.

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[1] Rama 550:1

[2] Michaber 554:5; Rama ibid; Hagahos Maimanis; Maggid Mishneh Taanis 5; Rambam Taaniyos 1:8

The reason: As it is greatly painful for them to fast. [Rama ibid] See P”M 550 A”A 2 that ideally, they are obligated to fast all four fasts, and it is only today that the fasts are due to a custom [as explained above that in times of peace it is not obligatory] that pregnant and nursing woman don’t have to fast, as they never accepted upon themselves this custom.

[3] Rama ibid; Siddur Yaavetz

[4] Rama ibid; M”A 550:2 that there is no prohibition for them to fast on a Taanis Tzibur Kavua being that everyone accepted the fast upon themselves, although by a Taanis for Geshamim its forbidden for them to fast, as rules Rama 575:5

[5] M”B 550:5

[6] Rama ibid; See Rama 575:5 that it is forbidden for them to fast; See M”A 550:2; Seemingly, if they do not feel well, it is forbidden for them to fast even a Taanis Tzibur Kavua, as it is detrimental for the child. However, see P”M 550 A”A 2 in explanation of M”A ibid, who implies even if they are in great pain, they may be stringent to fast. Vetzaruch Iyun.

[7] M”B 686:5; Kaf Hachaim 686:22 regarding Taanis Esther and the same would apply regarding the four fasts; See however M”B ibid in name of the Bach.

[8] See Makor Chaim of Chavos Yair 550 “No need to be stringent at all”; Siddur Yaavetz “They are exempt even if they are not feeling pain, and if they want they could be stringent”; Orchos Chaim of Spinka 550:4, in name of Yifei Lalev, in name of Bashamayim Rosh 91, and Teshuva Meahava that they are weak and have pain; Ashel Avraham Butchach 686 Mahadurah Tinyana; Hisorerus Teshuvah 1:6; Divreiy Yatziv 2:291; Piskeiy Teshuvos 550:1; 686:3 that so is the ruling of today’s Rabbanim.

[9] M”B 686:5; Kaf Hachaim 686:22 regarding Taanis Esther and the same would apply regarding the four fasts; See however M”B ibid in name of the Bach.

[10] Daas Torah 550 based on Y.D. 189; Kneses Yechezkal 71:30; Ashel Avraham Tinyana 550:1; Alef Hamagen 3; Piskeiy Teshuvos 550:1; See Nitei Gavriel Bein Hametzarim 5:1 footnote 1

[11] The reason: As until the passing of 24 months from birth a woman is considered to have weakness and shaken limbs. [Poskim ibid, based on Y.D. 189]

[12] See Nitei Gavriel ibid for Rabbanim who disagree with this ruling. [The Rav of Papa]; Rav Yaakov Yosef in name of Rav Bentzion Aba Shaul negated the above opinions