Miscarriage

My LMP was 15th March. I had little spotting on 1st June. I called my doc and went for pelvis scan. I came to know that there was no heartbeat. On my first scan on 6th week heartbeat was there but on my 2nd scan no heartbeat and it was showing 9weeks instead of 11 weeks. Doc called it the missed abortion. I had my D&E on 3rd june then. My question is: what are the causes of missed abortion? I used to work on laptop and sometimes i put it on my legs slightly touching to my stomach. Does it is a cause of abortion?? Kindly help me to understand! Thanks