Factors Associated with Changes in Body Mass Trajectories during Infancy: A Longitudinal Analysis in Japan

Abstract

Maternal behaviour and child birth outcomes have been shown to be associated with the risk of disease in children. However, little is known about their association with the trajectories of physical development. The aim of this study was to identify factors associated with body mass index (BMI) trajectories in Japanese toddlers. All 900 children born in Ibara City between 2006 and 2009 were enrolled in this study with their mothers. Children’s heights and weights were measured, as was BMI (weight [kg]/height [m] 2 ). Multilevel analyses examined the association of maternal behaviour (smoking, using formula milk, and leaving the child in a daytime nursery) and birth outcomes (weight, parity, and gestational age) with standardized BMI trajectories (z-score analysis). Average BMIs ± standard deviations at birth and at 1.5, 2, and 3 years were 12.6 ± 1.3, 16.8 ± 1.2, 16.1 ± 1.2, and 15.7 ± 0.1, respectively. Maternal behaviour was not associated with BMI trajectories. However, BMIs of low birth weight children at 3 years were significantly higher than those of other children ( β = 1.799, P < 0.001), although the increments slightly decreased over time ( β = – 0.035, P < 0.001). The BMI increments of prematurely born children also slightly decreased over time ( β = – 0.04271, P < 0.001). Other evaluated factors were not associated with BMI trajectories. Our results showed that low birth weight children are more likely to exhibit lower BMIs until 2 years of age; however, BMI rapidly rises afterwards. Longer follow-up periods are warranted to evaluate the consequence of the late-year rapid increases in BMI among low birth weight children.