Standards for children's height at ages 2-9 years allowing for heights of parents.

Charts are presented which give centile standards for boys' and girls' heights at ages 2 to 9 when parents' height is allowed for. Mid-parent height is used (i.e. the average of father's and mother's height). A comparison is made with results from the existing `parent-unknown' British standard charts. A child at the 3rd centile on the parent-unknown charts is (i) at the 20th centile on the new charts if his parents are small enough to average 3rd centile for adults, (ii) at about the 1st centile if his parents average the 97th centile. Conversely a child with 97th centile parents has only to be at the 25th centile for the population in the parent-unknown charts to be at the conventional 3rd centile limit of normal when parental height is allowed for. Thus the new standards result in considerably increased precision. Examples are given of normal boys with small parents who plotted outside the 3rd centile on the conventional charts but inside on the present charts. The differential diagnosis of genetic small stature is made considerably more straightforward by the use of these charts. The correlation coefficients are given at successive ages, from 1 month to 9 years, for child's supine length or height with mid-parent height and for mother-daughter, mother-son, father-daughter, and father-son relationships.