Birth weight and infant growth: “catch-up” vs. “slow-down” growth

Purpose To examine the relationship between fetal growth and infant growth at about 12 months Methods We conducted a retrospective cohort study based on 3,302 births followed up between 8–18 months from Louisiana Women, Infant and Children Supplemental Food Program, 1999–2001. Infant growth was measured as infant weight gain percent (IWG %) defined as the weight gain from birth to infant weight divided by the birth weight. Univariate and multivariate analyses were performed to compare the infant growth measures according to birth weight category and small, large, or appropriate-for gestational age (i.e., SGA, LGA, AGA) status. Results There was a reverse relationship between birth weight category and IWG%. The IWG % of birth weight categories of <1500 g, 1500 g-, 2000 g-, 2500 g-, 3000 g -, 3500 g-, and 4000 g- were 613.9%, 393.7%, 306.2%, 238.9%, 205.1%, 177.5%, and 151.3% respectively (p < 0.0001). The IWG % of SGA, LGA and AGA were 283.6%, 166.5% and 221.1% respectively (p < 0.0001). The IWG% remained markedly higher in SGA infants and lower in LGA infants at each month of infant age between 8–18 months. However, the low birth weight or SGA infants had lower Z scores and percentiles for weight for age, weight for length. Conclusion Low birth weight or SGA infants have a significant “catch-up” growth, whereas high birth weight or LGA infants have a significant “slow-down” growth. The potential impact of this growth change in SGA and LGA infants in the postnatal period on later life disorders need to be determined.