[General growth patterns and simple mathematic models of height and weight of Chinese children]

To explore the growth patterns and simple mathematic models of height and weight of Chinese children.

The original data had been obtained from two national representative cross-sectional surveys which were 2005 National Survey of Physical Development of Children (under 7 years of age) and 2005 Chinese National Survey on Students Constitution and Health (6 - 18 years). Reference curves of height and weight of children under 7 years of age was constructed by LMS method, and data of children from 6 to 18 years of age were smoothed by cubic spline function and transformed by modified LMS procedure. Growth velocity was calculated by smoothed values of height and weight. Simple linear model was fitted for children 1 to 10 years of age, for which smoothed height and weight values were used.

(1) Birth length of Chinese children was about 50 cm, average length 61 cm, 67 cm, 76 cm and 88 cm at the 3rd, 6th, 12th and 24th month. Height gain was stable from 2 to 10 years of age, average 6 - 7 cm each year. Birth length doubles by 3.5 years, and triples by 12 years. The formula estimating average height of normal children aged 2 - 10 years was, height (cm) = age (yr) x 6.5 + 76 (cm). (2) Birth weight was about 3.3 kg. Growth velocity was at peak about 1.0 - 1.1 kg/mon in the first 3 months, decreased by half and was about 0.5 - 0.6 kg/mon in the second 3 months, and was reduced by a quarter, which was about 0.25 - 0.30 kg/mon, in the last 6 months of the first year. Body mass was up to doubles, triples and quadruple of birth weight at about the 3rd, 12th and 24th month. Average annual gain was about 2 kg and 3 kg from 1 - 6 years and 7 - 10 years, respectively. The estimated formula for children 1 to 6 years of age was weight (kg) = age (yr) x 2 + 8 (kg), but for those 7 - 10 years old, weight (kg) = age (yr) x 3 + 2 (kg).

Growth patterns of height and weight at the different age stages were summarized for Chinese children, and simple reference data of height and weight velocity from 0 to 18 years and approximate estimation formula from 1 - 10 years was presented for clinical practice.