Growth delay is one of the main characteristics of Down's syndrome, but impaired growth velocity is particularly evident at certain stages of development.
Fetal growth has usually been reported to be relatively normal and the length of the neonate is often within normal limits, allowing for gestation. Some studies have reported prenatal growth delay, and a major Italian study comparing neonatal length, weight, head circumference, and weight/length squared reported all percentiles of growth variables lower in Down's syndrome infants except for weight/length squared percentiles.
At approximately the age of 6 months, when growth starts to become regulated by growth hormone, growth velocity usually begins to show a marked reduction from normal levels. Although for the Down's syndrome child the period between birth and 2 years and the period between 6 years and 10 years of age are times of accelerated growth, the deviation from normal levels remains significant. Slow growth velocity is also a particular feature of adolescence, although there is a pubertal growth spurt. The deviation of adult stature from the means of reference groups is greater than the deviations in early infancy.
The short stature in Down's syndrome seems to be mainly the result of impaired growth of the long bones of the leg, because sitting height measurements show that the growth of the vertebral column is closer to normal.
Why there is growth delay in Down's syndrome is not entirely clear, and several hypotheses have been advanced. Both human growth hormone therapy and zinc sulfate supplementation of the diet have been reported to accelerate growth.
Children with Down's syndrome tend to be not only shorter but also heavier than reference children. Charting the height and weight of a child with Down's syndrome using reference norms from the general population will show the abnormality of the growth pattern. However, it is more useful clinically to compare the height and weight of an individual against syndrome-specific norms because this will identify any deviation from the growth patterns of children with Down's syndrome.
Italian percentile charts have been drawn up for neonates with Down's syndrome based on a large sample of consecutively born infants. Specific growth charts for children with Down's syndrome have been constructed based on anthropometric assessments of US children, Sicilian children (thought to be representative of southern European children), and Dutch children (thought to be representative of northern European children). On average, the Dutch children were taller than the US children, and the US children were taller than the Sicilian children.
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