This is a scatter diagram with three curved lines superimposed. The horizontal axis shows gestational age in weeks, labeled 15, 20, 25, 30, 35, and 40. The vertical axis shows head circumference in millimetres, labeled 100, 150, 200, 250, 300, 350, and 400. The three lines are the solid lines from Figure 4, which represent males. The lowest line is labeled 5%, the middle line is labeled 50%, the uppermost line is labeled 95%, The lines start at the bottom left corner of the graph and rise in an almost straight line at first, the slope being about 15 millimetres per week of gestational age. The lines diverge slightly as they rise. Then the slope becomes less steep and the lines curve gently to a more and more gentle rise. There are several hundred points, most of which are between the two outer lines, with a few points being below the 5% line and a few above the 95% line, though they are never very far from the lines. The maximum distance is about the same as the distance from the outer line to the central line. Outside points are spread throughout the range. Points are particularly dense in the region gestation age 20 to 23 and 33 to 37 weeks.
Back to Measurement in Health and Disease: Reference Intervals and Centile Charts.
This page maintained by Martin Bland.
Last updated: 8 May, 2008.