[Ponderal index to describe a term neonatal population]

The terms small, appropriate, and large for gestational age cannot identify some alterations in body composition that might be identified by the ponderal index. The aim of the present study was to correlate birth weight with ponderal index to identify other patterns of intrauterine growth.

We performed a cross-sectional, descriptive study in which only one curve of the ponderal index was created for each week of gestational age (weeks 33 to 42) and including the 10th, 50th and 90th centiles because sex does not influence this index. This curve was based on 26,770 healthy infants born in Uruguay and registered in the Perinatal Information System of the Latin American Center for Perinatology. The database consisted of 194,908 infants born between 1995 and 1999. Exclusion criteria were mothers aged less than 15 years or more than 35 years, primiparas, those with > 4 pregnancies, smokers, a diagnosis of intrauterine growth retardation, chronic and pregnancy-related hypertension, cardiac problems, anemic and diabetic mothers, twins with congenital malformations, and intervals between pregnancies of less than 2 years or more than 5 years. Finally, the ponderal index of 43,189 neonates with a gestational age of 40 weeks was compared with the centiles of weight for gestational age to establish alterations in intrauterine growth.

Relating the ponderal index with birth weight revealed altered patterns of intrauterine growth in 13 %, 10.3 % and 7.9 % of neonates with appropriate, small and large birth weights, respectively. Moreover, six unusual patters were identified.

Use of the ponderal index curve for gestational age together with other growth curves improves the nutritional assessment of newborns. Further studies should be designed to develop strategies for the immediate, medium- and long-term management of identified risk groups.