Assuring Pediatric Nutrition in the Community

FREQUENTLY USED GUIDELINES:
Assessing Nutritional Status - Expected Weight and Stature

Height-age and weight-age
Estimating expected weight
Estimating ideal body weight
Midparent height

What are height-age and weight-age and how do I use them?
Height-age describes the age at which a child’s stature (length or height) crosses the 50th percentile on a growth chart. Weight-age describes the age at which a child’s weight crosses the 50th percentile on a growth chart. Height age is sometimes useful when estimating nutrient needs for catch-up growth or when there is a need to estimate an expected body weight. When using height age to estimate energy needs, it is critical to include other factors (e.g., physical activity, medical conditions) that contribute to energy needs as well.

How do I estimate expected weight?
Use height-age to estimate a child’s expected weight. This calculation is useful when a child is growing at an obviously inappropriate rate. Expected weight can be useful for estimating nutrient needs for catch-up growth or for weight loss.

Why is it difficult to estimate ideal body weight for a child?
Because children grow at different rates, it is impossible to quantify an absolute "healthy" weight based solely on age. Obviously, the desirable weight for a 108 cm, 6 year old girl is not the same as for a 120 cm, 6 year old girl, although both children are growing within normal limits.

Differences in body composition can make estimation of ideal body weight difficult. Also, a child’s ideal body weight changes as height increases with age. When it is necessary to estimate expected weight for height (e.g., to estimate nutrient needs for catch up growth or weight loss), height-age can be used.

Some sources recommend estimating ideal body weight based on age. This is not appropriate for many children; e.g., children who are short for their age.

What is midparental height and when should I use it?
Midparental height, also known as parent-specific adjustment for evaluation of length and stature, is a useful tool when an explanation for a child’s growth status is needed. If a child is very short or tall compared to his/her parents, adjustments can be made to the interpretation of his/her length or height measurement, aiding in assessment of nutritional status. Although only occasionally used, this adjustment is useful in differentiating between genetic and non-genetic (e.g., nutrition related) causes of short or tall stature.

For example, if a child is unusually short (e.g., less than the 5th percentile for age), but no environmental or medical factors explain the shortness, midparental height may be used to uncover genetic factors. (In this case, both parents might be short.) Conversely, a child may be growing at a rate that appears to be appropriate (e.g., between the 10th and 25th percentiles), but has parents who are extremely tall. When stature is adjusted to reflect parental height, a problem with growth may be revealed.

It is important to remember that ultimate height is achieved at different ages. For example, a relatively short parent may have achieved her height at a young age—thus, she was a relatively tall child. Her son or daughter may follow this pattern as well. Mid-parental height is not useful if a child’s parent is a teen—ultimate height may or may not have been achieved.

Himes JH, Roche AF, Thissen D, et al. Parent-specific adjustments for evaluation of recumbent length and stature. Pediatrics. 1985; 75-304-313.