head circumference

Brooklyn
I went for a ultra sound yesterday 20 weeks 3 days, today my doctor called to set me up another ultrasound with a specialist said they would call and have them call me sometime this week, she said the babies head circumference is around 6 days behind. 5th percentile everything else is perfect though. Anyone have anything similar what was the outcome? I'm trying not to worry but it's all I can think about!