Explosion of fetus at 17 weeks. Baby?

I did the first Transfer of IVF..it was successful and first trimester went really smooth...as soon I was about to complete 4 months, I started bleeding, was given tranexa and bleeding stopped but again after 4 days I started bleeding heavily and passed 2 big clots size of a palm...docs advised bed rest and progesterone and discharged me saying we cannot do much...then after 5 days I started having back pains and lower abdomen pain in intervals for 2 days...docs gave pain killers but pain wasn't stopping saying it was labour pain...then finally fetus expelled by its own and I delivered it at 17 weeks...Currently pls tell me why it happened...I am totally confused what could be the reason..pls guide me and help me..was IVF the reason for the bleeding clotting ? My placenta went for testing and it came back as acute chorioamniotis stage 2...pls explain why I lost my precious baby ???