133:13 If a pregnant woman smells a certain food and craves it, and it’s certain that if she is not given some of this food then she and the baby may be in danger, the following procedure applies. If she says, “I must have some” even though her face has not changed color, or if her face has changed color even though she hasn’t said anything, then we tell her quietly that today is Yom Kippur, since this will sometimes calm her mind. If she is not calmed by this, we feed her thus: first, we give her a taste such as by dipping a finger in gravy or something similar and putting it in her mouth because sometimes one drop is enough to do the trick. If this is not the case, then she is given less than the restricted amount. If this still hasn’t calmed her mind, then we give her as much as she needs. Similarly, any person whose face has changed color because of the smell of food is considered to be in danger and we feed him as described above. However, as long as his appearance has not changed, we don’t feed him, even if he says “I need it.” (One may only be fed until his mind is settled, he must then resume the fast – Mishnah Brurah 617:7. A sick person is simply fed as the doctor instructs – MB 617:4.)
133:14 The parameters for a pregnant woman or one who is dangerously ill eating and drinking on Yom Kippur, or violating yom tov for them, are the same as the parameters for violating Shabbos. The difference is that when it comes to eating and drinking, even if several doctors say that he doesn’t need to, or even if they say that eating or drinking would be detrimental but the patient says that he needs to, and even if he says that he is not yet in danger but that if he doesn’t eat he will get sicker and then be in danger, in all these cases, we listen to the patient and feed him (after reminding him that it’s Yom Kippur, just in case he forgot – MB 618:5). (Some parameters of this law only apply if the patient brought it up on his own, not if another person suggested it to him. See Bi’ur Halacha 618:1 s.v. v’im.) This is because, when it comes to eating and drinking, the patient is the best judge of his own situation.