Nutritional assessment of very low birth weight infants: relationships between anthropometric and biochemical parameters.

OBJECTIVE Analyze the importance of biochemical data and their relationship with anthropometric data in the longitudinal nutritional assessment of very low birth weight infants. METHODS A prospective cohort study was performed on 55 very low birth weight preterm infants (birth weight < 1.500 g and < 37 weeks of gestational age). Measurements of weight, length, head and mid-arm circumferences, mid-arm circumference: head circumference ratio, ponderal index, and body mass index. Serum prealbumin and retinol-binding protein were studied as biochemical parameters. All variables were collected at birth and days 14 and 28 of life. RESULTS The infants presented a mean birth weight of 1,076.7 +/- 286 g and mean gestational age of 30.7 +/- 2.1 weeks. At birth, the mean serum prealbumin was 7.0 +/-1.7 mg/dl and mean retinol-binding protein was 1.3 +/- 0.4 mg/dl. There was a significant increase in all variables studied from birth to day 28. According to nutritional adequacy, there were no differences between appropriate and small for gestational age infants neither in the anthropometric nor in the biochemical data. The anthropometric measurements did not correlate with biochemical parameters. The serum protein concentrations were converted to serum protein mass (SPM) as follows: SPM = serum protein concentration X (100 X weight) X (1- hematocrit)] since the studied proteins are largely intravascular and the protein mass would be a more accurate index of nutritional status. The SPM of both protein and anthropometric parameters were correlated, except for the ponderal index. CONCLUSIONS The serum protein mass of the prealbumin and the retinol-binding protein were better nutritional markers in the serial nutritional assessment of very low birth weight infants during neonatal period than the serum protein levels.