Is a 2nd time around blighted ovum possible? Or likely?

I have a hard time getting pregnant & staying pregnant. My first pregnancy ended at 7 weeks with a spontaneous miscarriage, I had a 2nd pregnancy healthy & full term, my 3rd ended at 10 weeks with what the doc said was an empty sac (blighted ovum), and then a 4th pregnancy full term & healthy. I am now 8 1/2 weeks pregnant & I'm going to the doc on Monday for my 1st ultrasound. How likely is it to have a 2nd blighted ovum? Has anyone ever had 2? I am just really concerned through my pregnancies because of the record that I've had in the past! I hope everything will be okay! And thanks for any help!!