Factors related to patterns of body mass index in early infancy: 18 month longitudinal study.

Background Children with early adiposity rebound (AR), measured using individual body mass index (BMI) growth curves, have an increased risk of metabolic disease as adults. The children with early AR, however, are not fully characterized. The aim of this study was to investigate the prevalence and characteristics of the infants who develop early AR. Methods A total of 1248 full-term children and their mothers participated in the present study. Pre-pregnancy, prenatal, birth, 4 month and 18 month records were collected. Children were classified into two groups: a decrease (D) group, in which the 18 month BMI was lower than the 4 month BMI (n = 1097), in keeping with the standard BMI percentile curve, and an increase (I) group, in which the 18 month BMI was higher than the 4 month BMI (n = 151). Results Although children in both groups had similar body size at birth, those in the I group had a lower weight at 4 months and higher weight at 18 months than those in the D group (P < 0.001). Fewer mothers in the I group exclusively breast-fed their infants (P = 0.012). These characteristics of infants in the I group suggested a pattern of low fatness level followed by rapid increased fat gain. Conclusions Approximately 10% (151/1248) of infants did not follow the standard BMI percentile curves between 4 months and 18 months of age. They were more likely not to be exclusively breast-fed. This finding further stresses the importance of breast-feeding in early infancy.