Waiting for a Natural Miscarriage - How Long?

Hi, I was diagnosed 2 weeks ago with a blighted ovum and choose to have a natural miscarriage. It has been 2 weeks now and I have had very slight spotting the last 3 days. I only see a tiny bit of blood tinged discharge each day then it stops for the rest of the day. I am wondering, for those that had a natural miscarriage, how long the spotting took place before the miscarriage happened? I don't have any cramps at this point. Nervous I will have to have a d&c as my obgyn has given me until next week to finish miscarrying as she is worried about infection.