I am suffering from repeated missed abortion for 2 times. I am trying to understand what is the root?

Many causes. The most common cause of first trimester abortions is chromosomal abnormalities. Mother nature has a very rigid system in place that makes sure that even the tiniest issues early on lead to termination of pregnancy. You will need an OB - gyn evaluate you for causes including advanced age, prior hx of stds, underlying medical conditions, etc.