Abu al-Zinad (may Allah have mercy on him) reports from the jurists of Madinah (the Successors) (may Allah have mercy on them) that they used to say, concerning a man who strikes a woman and causes her to miscarry: If it is miscarried dead, a fine (ghurrah) is due for it; and if it is born alive and dies afterwards, the full blood money (diyah) is due. And they used to say: Whoever kills a pregnant woman while the child is still in her womb, only the woman's blood money is due, not the child's.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16422