Thank you very much for your question. It is our pleasure to answer it.

In the name of Allah, We praise Him, seek His help and ask for His forgiveness. Whoever Allah guides none can misguide, and whoever He allows to fall astray, none can guide them aright.

First of all, it should be noted that if the miscarried fetus has taken human form – i.e. has hands, legs, and other organs – then the blood that a woman discharges because of this is postpartum bleeding. The least period for a fetus to take human form is 80 days. In such cse, the blood that will follow it shall be called nifas (postpartum period). The maximum time of nifas is forty days and there is no limit of its minimum time. It is prohibited to offer salah during nifas. But if the formation of the fetus parts is not complete and rather it was still embryo, then the blood following its abortion shall be of haid (menstruation) or istihadah (prolonged morbid bleeding) i.e. if it continues less than one day and night then you should wash your private parts before wudu and you prayer is valid. But if it continues one day and night or more provided it did not proceed 15 days, then it shall be counted as haid and prayer shall be exempted during it. 

Hence, in your case dear sister, you should wait see if it is the blood of haid (menses) then you should stop praying and fasting and repeat that day of fasting after you become clean. However, it is the blood of istihadah, then you continue praying and fasting and you do not have to repeat the fasting of that day because it is valid. 

And Allah knows best.