Short- and long-run associations between birth weight and children's height.

Much evidence suggests that the 1000 days spanning from conception to children's second birthdays are critical for physical development. Whether influence of the exposures occurring during this window lasts later in life is unclear. Our study investigates changes in associations between birth weight and height, one measure of physical development, over different life-stages and whether greater household wealth promotes better growth for low birth weight (LBW) children. Using longitudinal data from Young Lives, we analyzed associations between birth weight and physical growth and examined differences across ages and by household wealth for 3999 children from Ethiopia, India, Peru, and Vietnam. At 6-18 months, LBW children had 0.53-SD (Standard error [SE]: 0.08) lower HAZ. Over time, the gap between normal and LBW children narrowed significantly to 0.21-SD (SE: 0.05) and 0.24-SD (SE: 0.05) at 4-5 years and 7-8 years, respectively. Prenatal experiences are most salient in establishing the greatest height deficits within the first year. Although disparities in height are reduced in the first year, height differences at age 4-5 years remain at 7-8 years of age. Even among wealthier families, there was no recovery in height for LBW children during the first year and no catch-up growth for these children in later childhood. These findings suggest that prenatal conditions, reflected in birth weight, are more important in setting height trajectories in comparison to postnatal factors, which do not help children recover fully from early growth deficits.