umbilical cord around neck

I am 35 weeks and had a growth ultrasound today. The ultrasound tech said the baby's umbilical cord is wrapped once around her neck. She assured me it's nothing to be concerned or stressed about unless it's wrapped twice or more. I see the doctor in a few days so I plan to ask more questions then. Has anyone else had this experience? How do you know when it's wrapped twice... will the heart rate drop? Should I push for another ultrasound soon to see if there are any changes?