הכל חייבים להתענות ארבע צומות הללו ואסור לפרוץ גדר: הגה מיהו עוברות ומיניקות שמצטערות הרבה אין להתענות (הגהות מיימוני והמגיד פ"ה) ואפי' אינן מצטערות אין מחוייבות להתענות אלא שנהגו להחמיר ודוקא בג' צומות אבל בט' באב מחויבות להשלים (כדלקמן סי' תקנ"ד סעיף ה'):

The (legal) distinction that there is between Tisha B'av to the other fasts, and in it there are 4 paragraphs. All are obligated to fast on these Four fasts, and it is forbidden to break the fence (i.e. not fast) Rema: However, those who are pregnant or nursing that are very distressed, do not fast [Hagaos Maimoni and the Maggid Chapter 5]. And even if they (the above) are not distressed, they are not obligated to fast, rather customarily they are strict. (This lack of obligation for those in a lack of distress) is specifically on the 3 fasts, but Tisha B'av, they are obligated to complete (the fast) [like that brought in Siman 554 Paragraph 5]

These fast except for Tisha B'av one is allowed to wash, anoint, wear shoes, and have marital relations. And it is unnecessary to stop (from eating) when it is still day (in the case the 3 fasts when it is still night and the fast has not started yet).

3. All four fast if they fall on Shabbos, they are pushed to after Shabbos. Rema: If they fall on the eve of Shabbos, we read in the morning and afternoon prayers the parsha of Vyachel (Exodus 32:11 and on) [Bais Yosef] If there is a wedding on the day of the fast on the eve of Shabbos, the custom is pray the afternoon prayers and read Vyachel and then afterwards do the Chuppah ceremony [see Siman 249 Paragraph 4 if one completes the fast].

4. On Shabbos before a fast, a Community Representative (Shaliach Tzibur) announces the fast except for Tisha B'av, Yom Kippur, and the Fast of Purim (Taanis Esther). The remainder is forces (אכ"ף - Aleph - tisHA bav Kof - yom KIppur Geh - Purim) on him his mouth. (see Proverbs 16:26) Parentheses the custom of Ashkenazim is not to announce even one of them (of the fasts).