Table 1.
Demographic data and anthropometric variables of the subjectsa
| Variables | Total | Boys | Girls | Pb |
|---|---|---|---|---|
| N = 15,324 | N = 7919 | N = 7405 | ||
| Age (y), n (%) | 11.54 ± 2.59 | 11.49 ± 2.60 | 11.59 ± 2.58 | .579 |
| 7 | 938 (6.1) | 506 (6.4) | 432 (5.8) | .220 |
| 8 | 1444 (9.4) | 763 (9.6) | 681 (9.2) | |
| 9 | 1571 (10.3) | 818 (10.3) | 753 (10.2) | |
| 10 | 1843 (12.0) | 957 (12.1) | 886 (12.0) | |
| 11 | 1618 (10.6) | 861 (10.9) | 757 (10.2) | |
| 12 | 1734 (11.3) | 908 (11.5) | 826 (11.2) | |
| 13 | 1998 (13.0) | 979 (12.4) | 1019 (13.8) | |
| 14 | 2059 (13.4) | 1042 (13.2) | 1017 (13.7) | |
| 15 | 1358 (8.9) | 695 (8.8) | 663 (9.0) | |
| 16 | 576 (3.8) | 288 (3.6) | 288 (3.9) | |
| 17 | 185 (1.2) | 102 (1.3) | 83 (1.1) | |
| Weight (kg) | 41.42 ± 14.40 | 42.54 ± 15.63 | 40.21 ± 12.84 | < 0.001 |
| Height (cm) | 147.07 ± 15.49 | 147.89 ± 16.73 | 146.20 ± 13.99 | < 0.001 |
| BMI (kg/m2) | 18.58 ± 3.68 | 18.82 ± 3.89 | 18.33 ± 3.43 | < 0.001 |
| BAZ | < 0.001 ± 1.00 | 0.06 ± 1.05 | −0.07 ± 0.93 | < 0.001 |
| Birthweight (g) | 3281.0 ± 522.9 | 3338.9 ± 534.8 | 3219.2 ± 502.7 | < 0.001 |
| Gestational age (wk) | 38.44 ± 4.70 | 38.44 ± 4.81 | 38.43 ± 4.59 | .391 |
| Systolic blood pressure (mmHg) | 104.61 ± 12.10 | 106.08 ± 12.46 | 103.04 ± 11.51 | < 0.001 |
| Diastolic blood pressure (mmHg) | 65.12 ± 8.25 | 65.56 ± 8.62 | 64.64 ± 8.01 | < 0.001 |
| Hypertension, n (%) | < 0.001 | |||
| Normal | 13666 (89.2) | 6958 (87.9) | 6708 (90.6) | |
| Abnormal | 1658 (10.8) | 961 (12.1) | 697 (9.4) | |
| Birth weight category (g), n (%) | < 0.001 | |||
| < 2000 | 236 (1.5) | 124 (1.6) | 112 (1.5) | |
| 2000–2499 | 490 (3.2) | 217 (2.7) | 273 (2.7) | |
| 2500–2999 | 2398 (15.6) | 1066 (13.5) | 1332 (18.0) | |
| 3000–3499 | 6445 (42.1) | 3084 (38.9) | 3361 (45.4) | |
| 3500–3999 | 4095 (26.7) | 2350 (29.7) | 1745 (23.6) | |
| ≥ 4000 | 1660 (10.8) | 1078 (13.6) | 582 (7.9) | |
| Area of residence, n (%) | .890 | |||
| Chongqing | 3094 (20.2) | 1550 (19.6) | 1544 (20.8) | |
| Hangzhou | 3185 (20.8) | 1842 (23.6) | 1343 (18.1) | |
| Nanning | 2592 (16.9) | 1328 (16.8) | 1264 (17.1) | |
| Beijing | 1832 (11.9) | 928 (11.7) | 904 (12.2) | |
| Shanghai | 1545 (10.1) | 771 (9.7) | 774 (10.4) | |
| Tianjin | 3076 (20.1) | 1500 (18.9) | 1576 (21.3) | |
| Season of Birth, n (%) | .322 | |||
| Spring | 3563 (23.3) | 1866 (23.6) | 1697 (22.9) | |
| Summer | 3834 (25.0) | 1976 (25.0 | 1858 (25.1) | |
| Autumn | 4050 (26.4) | 2097 (26.5) | 1953 (26.4) | |
| Winter | 3877 (25.3) | 1980 (25.0) | 1897 (25.6) | |
Season of birth: spring = infants born in March, April and May; summer = infants born in June, July and August; autumn = infants born in September, October and November; winter = infants born in December, January and February
SD Standard deviation
aQuantitative data are expressed as the mean ± SD (standard deviation), and qualitative data are expressed as frequency (%)
bP for t tests or χ2 tests