Catch-up growth, muscle and fat accretion, and body proportionality of infants one year after newborn intensive care

We studied catch-up growth, muscle and fat accretion, and body proportionality at 4 and 12 months of age corrected for prematurity in 30 very low birth weight (VLBW) (<1500 gm), 30 low birth weight (LBW) (1500 to 2499 gm) and 30 normal birth weight (≥2500 gm) infants who required newborn intensive care. At 4 and 12 months, the VLBW infants had significantly lower mean weight and length (p<0.01), but not lower occipitofrontal circumference percentiles, than the LBW and normal birth weight groups, and showed no catch-up weight or length growth between 4 and 12 months. All three groups had significant increases in mean upper mid-arm circumferences, mid-arm muscle circumferences, and arm muscle areas between 4 and 12 months. Mean mid-arm muscle circumferences and arm muscle areas were similar among the three groups at 4 months but became significantly stratified by birth weight groups by 12 months, with VLBW infants having the lowest mean value. In contrast, analysis of fat stores by triceps skin-fold thickness and arm fat area demonstrated no significant increases in any group between 4 and 12 months, except for arm fat area in the LBW group. The VLBW infants had significantly less fat than normal birth weight infants at 4 and 12 months. All three groups had proportional growth at both visits, as assessed by mid-arm circumference/head circumference ratio and weight-length percentile for age. The VLBW infants were significantly lighter for their length than normal birth weight infants. We conclude that VLBW infants have no first-year catch-up growth, remaining smaller than higher birth weight infants, although appropriately proportional. Somatic growth during the first year is due more to muscle than to fat accretion, especially in VLBW infants.