Should a pregnant woman fast on the 17th of Tammuz and Tisha B'Av?

Greetings,

You are exempt from fasting on the 17th of Tammuz; however, it is advisable not to eat luxurious food but only basic food to sustain the fetus. On Tisha B'Av, you are obligated to fast unless a doctor tells you that it is dangerous to do so in which case you should consult with your local Rabbi.

Sources:

Shulchan Aruch (Orach Chaim 556:5). The Rema (Orach Chaim 554:1) wrote that only pregnant women who suffer greatly do not fast on the four fasts. Nevertheless, many poskim in recent generations have written that all pregnant women generally experience discomfort, and they should not fast on the four fasts and Taanit Esther, and they are permitted to eat immediately in the morning (Piskei Teshuvot there 1).

The definition of a pregnant woman is from the time the fetus is recognized, that is, when three months have passed in her pregnancy. Nevertheless, it is possible to be lenient even after forty days for the creation of the fetus if she feels discomfort, and before that, one should not be lenient unless she suffers greatly or feels weakness (see Mishna Berura 554:3, and Chazon Ovadia on the four fasts, page 59). There are those who are lenient in any case even before forty days for the creation of the fetus (Orach Tzion part 3 page 250, s.v. And behold, in Mor and Ktzi'ah).

Best regards,

Hillel Meirs