What does it mean if a baby's head is in the 50th percentile?

What does it mean when the doctor examines your baby and reports that his head size measures in the 50th percentile?

These percentiles refer to how your child compares to other children the same age. So if your baby's head measures in the 50th percentile, then half the children his age have bigger heads and half have smaller heads. Any measurement's percentile - whether it's head circumference, body length, or weight - is meaningful only when compared over time. If a baby's head falls into the 50th percentile for the first two years, that means it's growing normally; if it drops to a lower percentile or rises to a higher one, there's cause for concern. I'm sure your baby is above average in many ways, but the size of his head is indeed average. Believe me, it has nothing to do with his intelligence!