Yosef Karo

“ Rem"a Note: If these fell on the day before Shabbat, we [still] read 'Va-ya-chel'{Torah reading for fasts} (Beit Yosef) . If there is a Chuppah on the day of the fast which is [also] the day before Shabbat, we are accustomed to pray Mincha and read 'Va-ya-chel', and after this we perform the Chuppah (look at Siman 249, Seif 4 about if we complete the fast) :
סעיף ג
כל ארבעה צומות הללו, אם חלו להיות בשבת, נידחין לאחר השבת.
הגה: ואם חלו בערב שבת, קורים בשחרית ומנחה ויחל (ב"י) . ”

“ Shulchan Aruch Orach Chaim 550 The differences that exist between the ninth of Av to other fasts
הבדל שיש בין ט' באב ליתר צומות
550:1 All are obligated to fast on these four fasts, and it is forbidden to "breach the fence" {to make a break in the wall of Minhag}.
Rem"a Note: However for women who are pregnant or feeding who are in great discomfort, they oughtn't fast (Hagehot Maymonyot and the Maggid [Mishna] ) . [Furthermore] even if they are not discomforted, they are not obligated to fast, only that the custom has become to be strict. ”