GROWTH AND BODY-COMPOSITION OF PRETERM, SMALL-FOR-GESTATIONAL-AGE INFANTS AT A POSTMENSTRUAL AGE OF 37-40 WEEKS

In order to understand the nutritional status of preterm, small-for-gestational-age (SGA) infants in the early postnatal period, the growth and body composition of preterm, SGA infants was followed prospectively from birth to the postmenstrual age of 37-40 weeks. The infants were stratified into different groups by gestational age, clinical condition and body proportionality. In each subgroup, the growth and changes in body composition of SGA infants were compared with appropriate-for-gestational-age (AGA) infants of a comparable postmenstrual age. At birth, the SGA infants of both the 31-33 and 34-36 week gestational-age groups were smaller than AGA infants in all body measurements, including arm area (AA), arm muscle area (AMA) and arm fat area (AFA). When the preterm SGA infants had grown to the postmenstrual age of 37-40 weeks, the amount of fat they had accumulated was as much as, or more than that in term AGA infants. Yet, they had less muscle mass and their body weight, body length and head circumference were less than those in term AGA infants. This pattern of growth and the changes in body composition had been persistently observed in SGA infants of different gestational-age groups, different clinical status and different body proportionality. Differences between postnatal enteral nutrition and placental nutrition, or different energy utilization, in preterm SGA infants are hypothesized to account for these observations. The growth of less mature (31-33 weeks gestation) SGA infants and those preterm SGA infants with an eventful clinical course was suboptimal as compared with other SGA infants in the same subgroup. In this study, the weight to length ratio (WLR) was used to define the status of nutrition in preterm SGA infants: WLR less-than-or-equal-to 2 S.D. or > 2 S.D. off the reference mean. Infants in both groups showed some catch-up growth in body weight. Yet, at near-term their body weight were still more than 2 S.D. below the mean of term AGA. In each gestational-age group, the growth of these two body-proportionality groups did not differ from each other except for the low WLR group of 34-36 weeks gestation which had a significantly lower body weight and skinfold thickness than the group with a normal WLR. Multiple regression analysis revealed that skinfold measurements of preterm SGA infants at birth is the best factor for determining the body weight gain at near-term. After use of the skinfold thickness was set aside, WLR became the most important factor. The results of this study highlight the importance of evaluating the body composition of growing preterm SGA infants to assess their nutritional status.