Pregnant and nursing women:[1]

A pregnant or nursing woman must fast on Yom Kippur for the entire day [just like any other person]. [There is no allowance for them to eat or drink less than the Shiur, unless it is a case of danger, as will be explained. This applies even in today’s times.[2] If a woman fears she may have a miscarriage due to the fast, she is to speak with her doctor and with a competent Rav. The Rav is to review her miscarriage history[3], and take note of any warnings from her doctor.[4] If a doctor told the woman it is forbidden for her to fast due to fear of miscarriage, she is to verify with the doctor whether eating and drinking less than the Shiur will suffice to prevent danger. Likewise, she is to verify whether she could fast if she remains in bed for the entire duration of the fast.]

Q&A

If a pregnant woman began to have contractions, is she to break her fast?

The following is the general Rabbinical directive, in cases that a doctor has not directed otherwise: 

From beginning of pregnancy[5] up to 9th month:[6] If a pregnant woman prior to the completion of her 9th month [before week 37 from conception[7]], feels contractions that can lead to miscarriage or early birth, or feels pressure to push out the baby, then she is to eat in accordance to the Shiurim dictated below. If eating the Shiurim does not suffice, she may eat and drink any amount of food until her body calms down.

After the 9th month:[8] A pregnant woman who has completed her 9th month [past week 37 from conception[9]] is not allowed to break her fast unless she has entered into active labor to the point she cannot walk, is on the birthing stool, or has broken her waters, just as is the law regarding transgressing Shabbos. When she reaches this point, she may eat regularly.[10] However, prior to reaching this state, she may not eat or drink even less than the Shiur, even if she feels contractions and is in the midst of labor[11], unless a doctor directs her to do so due to fear for her life or the life of the child.

Must a nursing mother who needs milk for her infant, fast?[12]

Yes. She is to do everything possible to fast on Yom Kippur, arranging a milk substitute for her child, or pumping milk the days before the fast. In a case that the child refuses to drink anything else other than through nursing, a Rav is to be contacted.

Practical list of Shiurim for food and drink for a pregnant woman:

• Food:[13] A pregnant woman who may eat less than the Shiur, is to eat less than the size of a Kusebes, which is less than 30 cc and 30 grams, within the amount of time it takes to eat a Peras of bread, which is nine minutes: The food is measured based on volume and[14][15] Hence, the Shiur is [less than[16]] the amount of food to fill 30 cc in a measuring cup [or typical match box], and this amount itself is not to weigh more than 30 grams.[17] One is not to eat more than this amount of food within nine minutes.
• Drink: A pregnant woman who may drink less than the Shiur, is to drink within nine minutes less than the amount of water that can fill one cheek. Hence, before Yom Kippur, he is to fill a cheek with water, pour it into a cup, and mark the water level on the cup. When there is Halachic need to drink based on the Shiurim, one is to drink less than this marked amount of liquid within every 9 minutes. One is not to drink the exact amount marked, as this is the Shiur Kareis for liquid.

The amount of time to eat the Shiurim:

All the food and liquid that one consumes within nine minutes is counted as part of the Shiur. Meaning, that one should make sure not to eat the more than the Shiur of liquid or food within nine minutes, and hence the shiur restarts every nine minutes after completing eating or drinking less than the Shiur. If nine minutes is too long of an interval, one may go down to 8, 7.5, 6, 5, 4.5,4 minutes, as is medically necessary.

Preparing the Shiurim before Yom Kippur:[18]

A pregnant woman is to prepare the Shiurim before Yom Kippur. She is to fill one cheek with water and place it into a cup and then mark the water level. She is to mark on a cup the 30cc level mark for the sake of measuring food and liquid.

How to measure the food:

One is to crumble the food and enter it into an area which holds 30cc, which is the common size of a match box.

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[1] 617/1; Michaber 317/1; Pesachim 54b

[2] Tzitz Eliezer 17/20; Teshuvos Vehanhagos 2/292; Piskeiy Teshuvos 617/1; Rav Ovadia Yosef

Opinion of Rav Fisher: Rav Yaakov Yisrael Fisher [brought in Sefer Pnei Baruch; Piskeiy Teshuvos 617 footnote 1] was of the opinion that today pregnant women no longer have to fast, and may eat less than the Shiur on Yom Kippur, due to fear of miscarriage. Practically, this ruling is not accepted amongst Poskim or Moreh Horaas and rather each case must be judged individually by a competent Rav. [Poskim ibid] However, Rav Yaakov Yosef ruled after a thorough investigation amongst doctors, and discovering a dispute amongst them as to the dangers of fasting, that regarding Tishe Beav which is a Rabbinical fast, one may be lenient, while regarding Yom Kippur one is to be stringent.

[3] Some Poskim permit a woman to eat and drink less than the Shiur if she already miscarried twice in the past. [Tzitz Eliezer ibid; Pnei Baruch in name of Orchos Chaim 617/1; Daas Torah 317; Piskeiy Teshuvos 317/1; Poskim in Nitei Gavriel 38/6]

[4] Rav SZ”A ruled one may allow a woman to eat less than the Shiur if her Dr. says that the fast can lead to miscarriage, or an early birth that is prior to the 9^th month. [Piskeiy Teshuvos 617 footnote 2]

[5] From when is a woman considered pregnant in this regard? There is no difference in this regard whether she is in the beginning or end of her pregnancy. [M”B 617/1] The laws of fasting relavent to a pregnant woman begin to apply from the moment she knows she is pregnant, even if this is prior to the passing of 40 days from the time of conception. [Daas Torah 617/1; Sheivet Halevy 7/80; Nitei Gavriel 38/4] However, there are Poskim who question whether prior to 40 days we allow her to break her fast to prevent miscarriage. [Shaar HaTziyon 617/1; See also M”B 550/3; Kaf Hachaim 550/5]

[6] Ruling of Rav Asher Lemel Cohen

[7] See coming footnotes for explanation

[8] M”B 617/9; Mamar Mordechai 617/3; Alef Lamateh 617/5; Sdei Chemed 3/2; Meishiv Halacha 242; Minchas Yehuda 29; Nitei Gavriel 38/5; so ruled Rav A. L. Cohen

[9] According to Halacha, a child is considerd premature, and an 8^th month child, until nine full months have passed from conception. [See Y.D. 374/8; See Meil Tzedaka 5, brought in Pischeiy Teshuvah 374/9 that we follow the Hebrew months in this regard, and not a number of weeks or days. Thus, since the months vary between 29 and 30 days, determining how many weeks/days need to pass depends on how many days were in each of the nine months of her pregnancy. If, for example, there were five 30-day months and four 29 day months, then it is exactly 38 weeks, which is 266 days. If however there were more or less than five 30 day months, then it would be more or less than 38 weeks. Thus, we determine the completion of nine months based on the passing of Hebrew months, and not based on weeks or days.] Medically, however, a child is only considered premature if born prior to week 37 from her last period, which is approximately week 35 from conception. Nonetheless, a child born in week 37-38 from the last period is termed an “early term baby” and quite often the child is not yet developed enough to be born. It is only considered full term in weeks 39-40 from the last period, which fits the Halachic definition of 37-38 weeks from conception. 

[10] See Poskim ibid that compare a woman giving birth to a regular Yoledes within three days, of which the law is that she may eat regularly. However, see Minchas Yehuda and Nitei Gavriel ibid who record she is to eat less than the Shiur. Veztaruch Iyun.

[11] Piskeiy Teshuvos 317/1 footnote 3; Rav A. L. Cohen

The reason: As there is no danger involved for her or the child if she gives birth in her 9^th month, and hence there is no reason to permit her to eat in order to stop contractions.

[12] See Piskeiy Teshuvos 617/2

[13] Piskeiy Teshuvos 618; Shiurei Torah 3/10

[14] So is implied from Shiureiy Torah ibid towards end that by a food which weighs more than water it is to be less than 30 grams and less than 30 cc.

[15] Shiurei Torah 3/10, unlike Kaf Hachaim [and so rules Yalkut Yosef] who measures all based on weight; See Nishmas Avraham 612/2 footnote 16

[16] As 2/3 of an egg, which is the Shiur of the Kuseves [618/13] is 30 cc. [Shiureiy Torah ibid] Vetzaruch Iyun as Admur there writes 2/3 of an egg or a little more is the Shiur of a Kuseves, hence there is no exact Shiur. In any event seemingly to be on the safe side one is to eat less than that amount, and so is implied in Shiureiy Torah ibid. However, from Piskeiy Teshuvos 618/8 it is implied that one may eat that amount Vetzaruch Iyun.

[17] So is implied from Shiureiy Torah ibid towards end that by a food which weighs more than water it is to be less than 30 grams and less than 30 cc.

[18] Rav Cohen