P2C335: Comparing the Postnatal Growth of Infants Born with Low Birth Weight: Small for Gestational Age versus Appropriate for Gestational Age

Background: Infants born with birth weight less than 2.5 kg can be classified into appropriate for gestational age (AGA) and small for gestational age (SGA) based on their weight z score (WAZ) using Fenton standards. These infants may have different postnatal patterns of growth. This study described the postnatal growth pattern of low birth weight infants (less than 2.5kg) who were born AGA (WAZ >-2) versus those with SGA (WAZ <-2 (using Fenton growth standards) from birth to the age of 3 years.

Methods: Anthropometric measures (z scores) from birth to 2 years were measured in 150 infants born with birth weight < 2.5 kg but > 1.5 kg. They were divided into two groups based on Fenton preterm growth standards. The first group (AGA) with (WAZ) > -2 (n = 100), and the second group (SGA) with WAZ < -2 (n = 50). Postnatal growth data were evaluated based on the WHO growth standard without correction for prematurity.

Results: The gestational age (GA) was 32.2 +/- 2.5 weeks for the AGA group and 36.5 +/- 2.5 weeks for the SGA group. AGA infants had a progressive gain in WAZ during the first 18 months (from -3.15 to -0.0). Stable WAZ followed this period during the next 18 months of life. SGA infants had a progressive gain in WAZ (from -2.8 to -0.75) during the first three years of life. They were still catching up in WAZ during the 3rd year, and at the end of the second and 3rd years, SGA infants were significantly lighter (lower WAZ) compared to AGA infants (Figure 1).
AGA infants had a progressive gain in LAZ during the first 24 months (from -3.5 to -0.17). Stable LAZ followed this period during the 3rd year of life; however, SGA had a progressive gain in LAZ during the first three years (from -2.7 to -0.45). They were still catching up in LAZ during the 3rd year of life. At the end of the second year, they were significantly shorter than AGA infants. However, the difference in LAZ disappeared at the end of the third year (Figure 2). SGA had lower WLZ during the three years of postnatal life than AGA infants. Both groups had significant catch-up in head size (HCZ) during the first year of life. However, at the end of the second year, the SGA group had a significantly smaller head size (HCZ) than the AGA group.

Conclusion: Infants born < 2.5 kg classified AGA and SGA showed different postnatal growth patterns in WAZ, LAZ, and HCZ. At the end of the 3rd year, SGA infants were lighter but not shorter compared to the AGA group.