Hi Dear thanks for your question,the question you posed is difficult to answer,as you have not mentioned any thing in history except for absent fetal heart on ultra sound
and your on Hcg
,HCG is a hormone secreated by the placenta and Human chorionic gonadotropin
(hCG) therapy during early gestation may be useful in preventing miscarriage
since endogenous hCG is known to play a critical role in the establishment of pregnancy
.YOU MIGHT be having recurrent abortions, that is the reason your doctor has prescribed you HCG ,why you had an abortion,it is difficult say without history ,examination and investigation,however low HCG level are thought to be one cause of early abortion.