Blood clot between placenta and uterine wall?????

Hey.  This is my second pregnancy and I thought it was pretty normal until yesterday at my doc apt.  He informed me that the ultrasound showed a small blood clot between my placenta and uterus.  He said they typically go away, but we won't know for sure until my 20 week ultrasound. However, I've been told that if it is in that spot it typically ends in miscarriage.  Has anyone else ever had a blood clot there???   What was your outcome????   Thanks!!