A woman who was at the beginning of pregnancy had an accident and so she had a miscarriage after heavy bleeding. Should she complete her fasting or not? If she does not fast, would she bear a sin?
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu 'alyhi wa sallam, is His slave and Messenger.
Shaykh Ibn ‘Uthaymeen said: "We say that a pregnant woman does not have menstruation. Imaam Ahmad said that women know pregnancy by the cessation of menstruation. According to scholars, menstruation is something that Allaah The Almighty created in order to be nutrition for the fetus. This is why menstruation stops with the beginning of pregnancy. However, some women (very few) menstruate during pregnancy. For these women, this is considered menstruation because it lasts throughout the pregnancy and is not affected by pregnancy. Thus, this menstruation takes all the rulings of menstruation. The blood that emerges during pregnancy is either considered menstruation or not. If this blood lasts throughout the period of pregnancy it is considered menstruation, but if it does not last during the pregnancy and only emerges because of a certain incident such as having an accident or carrying something heavy and so forth, then it will not be considered menstruation, but rather irregular bleeding. This bleeding does not prevent women from fasting or praying as they take the same rulings of pure women. If, as a result of an accident, she miscarries the fetus, then scholars have said that the ruling depends on the fetus: If the fetus has been formed, then this blood would be post-partum bleeding and would take all the rulings accordingly. If the fetus is not formed, then this blood would be irregular bleeding and would not prevent her from fasting or praying or anything else. Scholars have said that the minimum time for the fetus to be formed is eighty-one days. ‘Abdullaah ibn Mas‘ood narrated that the Prophet, sallallaahu ‘alayhi wa sallam, said: “The creation of man is gathered in the form of a sperm-drop in the womb of his mother for forty days, then it becomes a clinging clot in a similar period, then it becomes a lump of flesh like that. After that, Allaah sends an angel who breathes life into it and writes his sustenance, lifespan, deeds and whether he will be happy or wretched.” Scholars have said that the fetus cannot be formed before this and usually formation does not appear until after ninety days, according to some scholars."
Allaah Knows best.