May a woman pump milk to bottle feed her baby if she can’t breast-feed him?
If a child is unable to breast-feed, such as if he is a preemie and cannot nurse, or if the child is sick or weak, or cannot nurse any other reason, and during the week the mother pumps her milk to bottle feed the child, then the following is the law regarding if this may also be done on Shabbos:
If it is still possible to nurse the child, then even if doing so entails difficulty, the mother may not pump her milk to bottle feed the child and she must nurse him on Shabbos. If the child will absolutely not nurse, then during the week the mother is to pump her milk in order to store for use on Shabbos, as will be explained below. If for whatever reason this was not or could not be done [such as if she has a small milk supply], then if there are no breastmilk Gemachim in one’s area [see below], and there’s nothing else available for the child to eat [such as formula, as explained below], then since there is possible danger involved for the child to go hungry, therefore, she may pump milk on Shabbos for the sake of feeding her baby from a bottle.
Baby formula-If available but not medically recommended: If formula or other breast milk alternatives are available, but one’s doctor states that he does not recommend it based on the health situation of this child, and that in his opinion the child needs specifically to be having mother’s milk, then the above allowance of pumping on Shabbos applies. If formula, or other supplements, are available and there is no medical reason for the child to avoid taking it instead of breastmilk, then it is forbidden for her to pump on Shabbos for this purpose. In all cases that one is unsure how the baby will react to the formula, one is to consult with one’s health care provider, and try to feed the baby some of the formula during the week to see the baby’s reaction. Some Poskim, however, are lenient and rule that there is no need to try feeding formula to the baby simply for the sake of not pumping on Shabbos, and only if one anyways gives him formula during the week is it forbidden to pump on Shabbos. This especially applies with a premature baby.
The amount of milk that she may pump at a time: Some Poskim rule that she should not pump out more than a Grogeres worth of milk at a time. Hence, she is to pump out less than a Grogeres worth of milk and feed it to the child, and then pump out another Grogeres worth and feed him it. She should not pump out more milk until the child is fed the previous milk that was pumped. However, other Poskim negate this and rule that it is permitted, and even Halachically advantageous, for her to pump as much as necessary for that Shabbos, in one session.
Using an electric pump versus hand pump: Ideally, even if a woman is required to pump her milk on Shabbos for the sake of feeding her child due to Pikuach Nefesh, she should only use a manual hand pump, [if an electric pump was not set up on a timer before Shabbos and a gentile is not available, as will be explained]. If, however, there is difficulty in doing so using a hand pump, or it is not available, then she may use an electric pump and even plug it in on Shabbos through a gentile, or using a Shinuiy. This preference of using a manual pump, however, only applies if the electric pump was not set up before Shabbos on a timer, however, initially it is better to use an electric pump that was set to a timer before Shabbos than to use a manual pump. [One is to plug in an electric pump before Shabbos and set it up on a timer to turn on at set intervals for her to pump her milk.] When using an electric pump, she should place the pump on her breast prior to it turning on, in order so it be considered like Gerama.
Pumping before Shabbos and storing the milk: In order to avoid the need of desecrating Shabbos through pumping the milk, a woman should pump during the week and store the milk in the freezer and the like in order to then use on Shabbos. There is no problem in the defrosting this milk on Shabbos, and one may even do so near a source of heat so long it cannot reach Yad Soledes. One may also place it in a bowl of Keli Sheiyni hot water in order for it to melt and become warm. However, one may not completely submerge it within the water if one intends for the milk to warm up.
Milk Gemachim: Certain communities have breast milk Gemachim for women who are not able to pump enough milk to feed their child. If such a Gemach is available, one is to use their milk rather than to pump on Shabbos.
 See Har Tzevi 201; Piskeiy Teshuvos 330:11; Shabbos Kehalacha 19:8
 Divrei Shalom 1;28; Piskeiy Teshuvos ibid footnote 82; However, see Shabbos Kehalacha 19:13-14 and Biurim 7 regarding using an electric pump that set up before Shabbos, and that in a time of great need she may do so, if she places it on her breast before it turns on.
 Although doing so involves a biblical transgression, one may transgress biblically for the sake of Pikuach Nefesh. [Admur 328:41]
 See Or Letziyon 2:36-8; Nishmas Shabbos 328:460; Piskeiy Teshuvos 330:11 footnote 83 that in today’s times that the formulas have tremendously advanced in their quality, one should not follow leniency of the Poskim in next footnote, and should always try formula first, after consulting with a doctor.
 Maor Hashabbos 14:61 in name of Rav SZ”A and Rav Elyashiv; Yabia Omer 9:32; Shabbos Kehalacha 19:9
 Har Tzevi 201, brought in SSH”K 36:22
 A Grogeres is 19.2 milliliters [Shiurei Torah 3:17], thus one is to squeeze less than this amount at a time; See regarding the shiur Chatas for pumping breast milk: Birkeiy Yosef 328:13 in name of Radbaz; Erech Hashulchan 328:13; Kaf Hachaim 328:204
 The reason: In order to avoid pumping the amount that would make one liable for a Chatas. [Har Tzevi]
 Shabbos Kehalacha 19 Biurim 5; Piskeiy Teshuvos 330:11 footnote 84
 As all the milk in the stomach of the child joins for the Shiur [Avnei Nezer 232; Ketzos Hashulchan 138 footnote 30], and hence pumping in intervals does not make this matter more lenient. [Shabbos Kehalacha ibid]
 In order to diminish the amount of times that she pumps. [Shabbos Kehalacha ibid]
 Some Poskim rule, that if a gentile is available, then it is better to use an electric pump through asking the gentile to plug it in, then to use a hand pump. [Shraga Hameir 3:7; Piskeiy Teshuvos ibid footnote 85]
 Piskeiy Teshuvos ibid and footnote 86
 Piskeiy Teshuvos ibid footnote 85; Shabbos Kehalacha 19:13-14 and footnote 23 and Biurim 7
The reason: As by an electric pump it does all the pumping, and hence she is only considered to have done one action of Melacha, while by a manual pump, every time she squeezes it, another Melacha is done.
 SSH”K 27:50 based on Chazon Ish 38:4; Shabbos Kehalacha ibid; Piskeiy Teshuvos ibid footnote 87; However, see Maor Hashabbos 14 footnote 105 that this is not Gerama at all; See also there and Toras Hayoledes 41:7 if placing one’s finger on the hole which causes it to turn on is considered Gerama or not
 Piskeiy Teshuvos 330:11
 See Admur 320:16; 318:25-27; Shabbos Kehalacha Vol. 1 p. 212
 See Admur 318:29; Michaber 318:17; Shabbos Kehalacha Vol. 1 p. 210
 See regarding the cooking prohibition, that it does not apply by milk in a Keli Sheiyni: Admur 318:12; Minchas Yitzchak 5:127 [unlike SSH”K 1 footnote 151 based on M”B 318:39]; See Poskim in next footnote regarding that the insulation prohibition does not apply in such a case if not fully submerged
 See Admur 318:23; Mahadura Basra for chapter 259 p. 878 in new Shulchan Aruch; M”B 258:2; Chazon Ish 37:17; Sheivet Halevy 5:31; Shabbos Kehalacha Vol. 2 page 65; Piskeiy Teshuvos 258:2