Hi..i Hve Missed Abortion In 3.5 Months And Ultrasound Report

hi..i hve missed abortion in 3.5 months and ultrasound report shows that there is 2.5 months n according to me its 3.5 mnths at 6.5 weeks we seen cardiac activity n after we hve dne ultrasound at 12 weeks n there is no any cardiac activity shown...so dctr suggest us to abortion n histopathology reprt result is that nacrotic decidual tissue and few hynalinized chorionic villi..so i wnt to knw the problm behind this...due to this happens