There are a few interesting Halachot that apply to Tisha B’Av this year, when the ninth of Av is on Shabbat, and the fast is נדחה, or pushed off to Sunday.
There is a general leniency to nursing or pregnant women. They should try to fast but if there is any discomfort, they are allowed to eat.
Another point to remember is that Havdala is said on Sunday night with only wine. We say Havdala in שמונה עשרה at Maariv and we also say בורא מאורי האש. If someone needs to break their fast early, they should also say Havdala.
Even though Shabbat is actually Tisha B’Av, the מנהג ירושלים is that there is no אבלות, mourning, at all, on Shabbat. Some say that we should not even sing לכה דודי to the tune of א-לי ציון. Therefore, no סעודה המפסקת or eggs in ashes. The fast begins before 7:29.