incomplete miscarriage

Hi
I've previously had 2 missed miscarriages and I had an incomplete mis 2 weeks ago.
I was 13 weeks and started to bleed lightly and when I went for the scan I was told that I was having an incomplete mis as there was tissue left measuring 7 cm. The consultant wasn't forthcoming but I saw on my notes that it said no sac, yolk or baby. So does this mean that the fetus had never developed or that the fetus was already in my birth canal on its way out? I was supposed to have a d & c but it passed naturally 5 days after I started bleeding.I've read about a blighted ovum so am getting a bit confused.
On my 2 missed misscarriages I did not have any pregnancy symptoms but on this last mis I felt properly pregnant