Rohrer’s Ponderal Index (PI) is an indication of a person’s weight relative to their height, and is used as a proxy measure of adiposity, similar to the Body Mass Index (BMI). PI is calculated as weight (kg) divided by cubed height (m3) (du V. Florey, 1970).
Compared to the more commonly used proxy for body fat BMI, (the person’s weight divided by the square of their height), PI better corrects for height, and therefore is a better estimate of adiposity, among newborn infants and also in the adolescent population (Peterson et al, 2017).
At birth, PI can be used to assess the pattern of fetal growth in small-for-gestational-age (SGA) infants (Armangil et al, 2011), by distinguishing symmetric from asymmetric intrauterine growth restriction, and quantifying the severity of asymmetry in growth-restricted neonates.
If using the metric system, PI is calculated as body weight divided by the cube root of height, where weight is in kilograms and height in meters.
PI = Weight (kg) / [Height (m)]3
Other variables might be needed for the interpretation of this index such as sex, age and gestational age, however population reference data on PI are not widely available.
In infancy, like the other growth indices, PI can be independently assessed by the percentile point achieved by a child relative to the healthy children of that age and sex in the same population. Median (or the 50th percentile) is regarded as a reference value, and 3rd and 97th percentiles as thresholds to indicate abnormally low or abnormally high values. A PI <10th percentile reflects fetal malnutrition; a PI <3rd percentile indicates severe fetal wasting. While a PI >90th percentile was defined as neonatal overweight.
Considerations relating to the use of ponderal index in specific populations are described in Table 1.
Table 1 Application of ponderal index in different populations.
|Infancy and lactation||Suitable.|
|Toddlers and young children||Not suitable as population reference not available.|
|Adults||Suitable, however BMI more commonly used.|
|Older Adults||Suitable, however BMI more commonly used.|
|Ethnic groups||Not suitable as population reference not available.|
Refer to section: practical considerations for objective anthropometry
Resources are dependent on the instruments/methods used to derive the raw data of height and weight.