[Growth velocity of preterm appropriate for gestational age newborns]

To assess the growth velocity of preterm appropriate for gestational age newborns through growth curves.

A longitudinal and prospective study was carried out at two state-operated maternity hospitals in Belo Horizonte. Two hundred and sixty appropriate for gestational age preterm infants with birth weight < 2,500 g were evaluated weekly for body weight, head circumference and length. Growth velocity curves were constructed based on the derivative of the mathematical equation of the Count's model applied to somatic growth. Two analyses were made in the present study: absolute velocity, i.e., weight gain (g/day), and head circumference and length gains (cm/week); and relative velocity, i.e., weight gain(g/kg/day), and head circumference and length gains (cm/m/week).

The curves of weight gain (g/day) were proportional to birth weight (the lowest and the highest birth weight neonates gained 15.9 and 30.1 g/day, respectively). The curves of weight gain (g/kg/day) were inversely proportional to birth weight with increasingly higher rates of weight gain between the first and fourth weeks (during the third week, the lowest and the highest weight newborns gained 18 and 11.5 g/kg/day, respectively). Later there was a drop, and by the 12th week the rates were similar for all groups (7.5 to 10.2 g/kg/day). The curves of relative velocity (cm/m/week) for head circumference and length were inversely proportional to birth weight; the lower weight preterm newborns had, the higher head circumference and length growing rates were, compared with those with more weight.

The relative velocity is the best parameter to describe the growth dynamics of preterm infants, especially of those with lower birth weight. Lower birth weight infants gained more weight, head circumference and length.