Blighted Ovum in second trimester

I just found out that I have a blighted ovum. I am supposedly 16.5 weeks. I went in for an ultrasound to double check my dates and found out right then that I was not carrying a fetus anymore. I am trying to wait and let my body flush it out instead of having a D&C. Is it common to have a miscarriage this late? If I don't get a D&C I wonder how long it would go on for. My OB/GYN is giving me a week to pass it on my own, but I want to know if there are any other mothers out there who have experienced such a late miscarriage and how you feel about it. I am upset because I thought that I was almost half done, and to go in thinking you get to see your baby for the first time to find out there is no baby, is quite devestating. Is there anyone who knows how I feel?