I am extremely confused about what my wife is going through with her miscarriage. I've tried talking to her OB-GYN when we've gone in for appointments but I leave more an more confused. I was hoping to get an answer here!

About 2 weeks ago my wife began feeling lower back pain (she was 8 weeks pregnant). We went into her doctor for an appointment and we were informed that she was about to miscarry. A blood test was taken. My wife had experienced no spotting or additional cramping until this week. We got a call from the doctor that her HCG level had dropped to zero and my wife has begun to bleed regularly and seriously.

Is it possible to have a HCG level of zero before the miscarriage even happens? How long should it take for normal HCG levels to return to 0?