Small head circumference at birth and early age at adiposity rebound

AimsThe adiposity rebound is the age in childhood when body mass index is at a minimum before increasing again. The age at rebound is highly variable. An early age is associated with increased obesity in later childhood and adult life. We have reported that an early rebound is predicted by low weight gain between birth and 1year of age and resulting low body mass index at 1year. Here, we examine whether age at adiposity rebound is determined by influences during infancy or is a consequence of foetal growth. Our hypothesis was that measurements of body size at birth are related to age at adiposity rebound. MethodsLongitudinal study of 2877 children born in Helsinki, Finland, during 1934-1944. ResultsEarly age at adiposity rebound was associated with small head circumference and biparietal diameter at birth, but not with other measurements of body size at birth. The mean age at adiposity rebound rose from 5.8years in babies with a head circumference of 33cm to 6.2 in babies with a head circumference of >36cm (P for trend=0.007). The association between thinness in infancy and early rebound became apparent at 6months of age. It was not associated with adverse living conditions. In a simultaneous regression, small head circumference at birth, high mother's body mass index and tall maternal stature each had statistically significant trends with early adiposity rebound (P=0.002, <0.001, 0.004). ConclusionWe hypothesize that the small head size at birth that preceded an early adiposity rebound was the result of inability to sustain a rapid intra-uterine growth trajectory initiated in association with large maternal body size. This was followed by catch-up growth in infancy, and we hypothesize that this depleted the infant's fat stores.