- Peninei Halakha
Pregnant and nursing women must fast on Tisha Be-Av, because only sick people are exempt from fasting on Tisha Be-Av, and pregnant and nursing women are considered healthy unless they feel unusually weak. However, pregnant and nursing women need not fast on the minor fast days since, technically, the prophets’ main enactment of these fasts was for times when Israel is faced with harsh decrees; when no such decrees exist, it is up to the Jewish people to decide whether they want to fast or not. Indeed, the Jewish people have accepted upon themselves to fast on these days until the Temple is rebuilt, speedily in our days. However, from the very beginning, the common practice has been that pregnant and nursing women do not fast on these days, because it is harder for them to fast.
Nevertheless, many pregnant and nursing women in Ashkenaz were stringent with themselves and fasted on the minor fast days. Perhaps they did this because of the harsh decrees that they experienced there. In any event, the prevalent custom today, even among those of Ashkenazic descent, is that pregnant and nursing women do not fast on the minor fast days. And even if a particular woman wants to be stringent, it is better that she refrain from doing so if she has trouble fasting. From the moment a woman knows that she is pregnant, she is exempt from the fast.
A nursing woman is exempt from the minor fasts as long as she is still nursing her child. Even if the child receives additional nourishment, the mother does not need to fast as long as she has not stopped nursing. Some poskim exempt all women from fasting for 24 months after giving birth, because, in their opinion, the exemption is not contingent upon nursing but on the trauma of childbirth, from which it takes 24 months to recover. In practice, most poskim rule stringently and require women who have stopped nursing to fast even on the minor fast days. This is the prevalent custom. However, one who wishes to be lenient has authorities on whom to rely, as several great poskim rule leniently on this issue.
 In general, a pregnant woman refers to one who is noticeably pregnant (c. three months pregnant). However, in the present case, the Aĥaronim stated that since a woman is in greater pain and at higher risk of miscarriage specifically during the first few months of pregnancy, a woman who knows with certainty that she is pregnant, based on a test or the like, is exempt from fasting. However, mb 550:3 and sht ad loc. 2 state that one may rely on this approach and be lenient before the fortieth day of pregnancy only if she is in great pain (as then she is considered sick). In my humble opinion, though, this ruling was based on technology available then, which could not produce certainty of early-stage pregnancy. However, if one knows with certainty that she is pregnant, the danger of miscarriage already exists, and it is clear that her aches are a result of her pregnancy. Therefore, like all pregnant women, she need not fast. Mikra’ei Kodesh (Harari) ch. 1 n. 10 states that R. Mordechai Eliyahu ruled likewise.
Rabbeinu Yeruĥam, Radbaz, and other poskim write that pregnant and nursing women may not fast on the minor fast days. Rema writes that such women have a custom to be stringent and fast. The Aĥaronim (Ĥayei Adam 133:6, ahs 550:1) divide pregnant and nursing women into three categories: healthy women have the custom to be stringent; those who experience some pain when fasting are exempt from the custom to be stringent, but are not prohibited from fasting; and those who suffer greatly may not be stringent. Nowadays, the prevalent ruling for Ashkenazic women is to refrain from fasting. See Piskei Teshuvot 550:1, which cites extremely lenient views, stating that all women who might give birth are exempt from these fasts, so that they have strength to give birth. Piskei Teshuvot also cites the view that such women should “redeem” the fast by giving charity. Most poskim do not accept this opinion, but one may use it as an additional reason to rule leniently in cases of uncertainty.
 The following authorities rule leniently: Maharsham, Da’at Torah 550; Yeĥaveh Da’at 1:35. See the previous note. According to the straightforward interpretation, however, only nursing women are exempt; this is the view of most poskim. R. Mordechai Eliyahu concurs in Hilkhot Ĥagim 24:35. For a summary of the various opinions, see Mikra’ei Kodesh (Harari) 1:4.