B O D Y P R O P O R T I O N S I N S M A L L F O R G E S T A T I O N A L A G E C H I L D R E N A F T E R R E C E I V I N G G R O W T H H O R M O N E T R E A T M E N T Introduction The common definition of small for gestational age (SGA) children refers to a birth weight below the 10th percentile for gestational age1. Researchers suggest that low birth weight followed by rapid weight gain during early postnatal life is associated with long-‐term risks for central obesity, insulin resistance and cardiovascular dis-‐ eases, known as the metabolic syndrome2,3. Other studies indicate that not only accelerated4, but also decelerated5 weight gain in these infants is associated with a risk on the metabolic syndrome. Therefore, an accurate follow up of the growth of SGA children is necessary and should be performed by a physician known with consequences of abnormal growth in childhood. This is even more important realiz-‐ ing that growth velocity in SGA children is different from normal weight children. In SGA children, both weight and length remain behind during their first year of life but thereafter most children show a catch-‐up growth in weight beyond the normal range for non-‐SGA children, which can be partly explained by a regression to the mean. However, a large part of the SGA children show faster acceleration in their weight gain compared to their length which discrepancy is estimated as an extra risk factor for overweight at the age of 5 years6. Those children who do not correct their length spontaneously are eligible for treatment with recombinant human growth hormone (rhGH). Treatment with rhGH based on the indication criteria reviewed by the Dutch Growth Research Foundation7, is an effective and safe approach to reduce the adult height deficit that short SGA children otherwise face8. In GHD children it is shown that besides its positive effect on growth, rhGH also influences metabolism9,10. The basal metabolic rate increases11, visible as a change in body composition by an increase in fat-‐free mass (FFM)12. rhGH treatment of SGA children also results in a decline in fat mass (FM) and an increase in FFM, which is consistent with the lipolytic and anabolic properties of rhGH treatment13. In a study of Hoos et al the change in body compo-‐ sition in GHD children was already detectable after 6 weeks of treatment with rhGH14 as measured by total body water (TBW) with the Deuterium dilution meth-‐ od. A nationwide study revealed that treatment with rhGH changes the body com-‐ position in SGA children too, but less compared to GHD children15. This can be pos-‐ sibly explained because SGA children have a reduced body fat percentage before treatment with rhGH in contrast to GHD children whose body fat percentage is increased16,17. In addition SGA children have a reduced sensitivity for IGF-‐1 (insu-‐ lin-‐like growth factor 1) unlike GHD children18. Therefore, in SGA children, a decrease in FM can hardly be expected and mainly an increase in FFM can be meas-‐ ured. Although the Deuterium method is accepted as a golden standard to measure TBW, in SGA children it seems therefore less accurate to estimate the effect of rhGH treatment. 61
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