2nd trimester loss and autopsy report

Tomorrow makes two weeks that I lost my baby boy I was 19 weeks but my baby boy heart stopped around 17 weeks no one knows why because on my past ultrasounds were normal and all my blood work was normal as well so they said that they will test my baby and also the placenta they keep telling me that it's not my fault and it probably was something that couldn't have been prevented but I still can't stop to think that it was my fault. Have you already received your autopsy report and what did they tell you what was the reason that your baby's heartbeat stopped when everything was going so well