Tawus (may Allah have mercy on him) says that Sayyiduna Umar (may Allah be pleased with him) sought counsel, then he narrated the full report and said that the Prophet (peace and blessings be upon him) gave a ruling concerning the fetus and the woman, and for the fetus he ruled "a male slave, or a female slave, or a horse."
So he narrated it mursal; and Amr bin Dinar narrated it from Tawus and made it the saying of Tawus himself.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16417