Underweight and Obesity in Low Birth Weight Children in Early Infancy in Japan

Introduction: Although there are several reports on the prevalence of underweight or obesity in low birth weight (LBW, <2.5 kg) children, there are few longitudinal studies from birth to early infancy. Methods: We enrolled 177 (93 boys) LBW and 2485 (1267 boys) normal birth weight (NBW, ≥2.5 and <4.0 kg) children. Height and weight data at birth and at 1.5, 3.5, and 5 years were obtained from mother-health child records. Underweight and obesity were defined as <5th percentile and ≥90th percentile of the body mass index (BMI), respectively, based on reference values for Japanese children. Results: LBW children had accelerated growth from birth to age 3.5 years, but at Age 5, both sexes had significantly lesser height and weight z-scores, with notably lesser BMI percentile scores for girls, compared with NBW children. The prevalence of underweight was significantly higher in the LBW children throughout the study period. There were no significant differences in the prevalence of obesity between the two groups, except for at birth. Multiple regression analysis revealed that small-for-gestational age was associated with underweight at Age 5 years. Conclusions: This study indicates that, up to Age 5, underweight is a more serious problem than obesity in LBW children. Our results suggest that careful observation of growth from early infancy is necessary to prevent the occurrence of underweight in early infancy.