- Ponderal index.

 

Ponderal index

The ponderal index (PI) is a useful tool to detect FGR, particularly in infants with asymmetric FGR.

PI is a ratio of body weight to length expressed as:

PI = [weight (in g) x 100] ÷ [length (in cm)]3

Ponderal index is recorded as a number in g/cm3, but there are also percentile curves for ponderal index.

Normal ponderal index is GA dependent, but is generally 2.2 to 3.0 g/cm3 (3rd and 97th percentile).

A ponderal index of <2 or <10% is abnormal and suggests asymmetrical FGR. Infants with constitutional or symmetric FGR typically have a normal ponderal index.

With normal growth, the PI increases gradually from 30 to 37 weeks gestation and then remains constant. Decreased growth of adipose tissue and skeletal muscle, the major contributors to body weight, results in a reduced PI. PI of less than the 10th percentile reflects fetal malnutrition; PI of less than the 3rd percentile indicates severe wasting.