Table 1.
Characteristics of the study participants
| Variables | No | Boys, n (%) | Girls, n (%) | χ2 | P value |
| Number | 62 715 | 32 629 (52.0) | 30 086 (48.0) | ||
| Age (year) | 2.76 | 0.948 | |||
| 3 | 2006 | 1023 (3.1) | 983 (3.3) | ||
| 4 | 8186 | 4250 (13.0) | 3936 (13.1) | ||
| 5 | 8481 | 4434 (13.6) | 4047 (13.5) | ||
| 6 | 8237 | 4286 (13.1) | 3951 (13.3) | ||
| 7 | 8133 | 4260 (13.1) | 3873 (12.9) | ||
| 8 | 8540 | 4431 (13.6) | 4109 (13.7) | ||
| 9 | 7494 | 3876 (11.9) | 3618 (12.0) | ||
| 10 | 6477 | 3402 (10.4) | 3075 (10.2) | ||
| 11 | 5161 | 2667 (8.2) | 2494 (8.3) | ||
| BMI category | 803.87 | <0.001 | |||
| Grade 3 thinness | 1637 | 752 (2.3) | 885 (2.9) | ||
| Grade 2 thinness | 2071 | 938 (2.9) | 1133 (3.8) | ||
| Grade 1 thinness | 6568 | 3001 (9.2) | 3567 (11.9) | ||
| Normal | 38 831 | 19 502 (59.8) | 19 329 (64.3) | ||
| Overweight | 8614 | 5292 (16.2) | 3322 (11.0) | ||
| Obesity | 2514 | 1696 (5.2) | 818 (2.7) | ||
| Severe obesity | 2480 | 1448 (4.4) | 1032 (3.4) | ||
| Birth weight category (g) | 19.88 | <0.001 | |||
| <2500 | 3359 | 1622 (5.0) | 1737 (5.8) | ||
| 2500–4000 | 59 356 | 31 007 (95.0) | 28 349 (94.2) | ||
| Neonatal characteristics | |||||
| Pregnancy term (weeks) | 19.22 | <0.001 | |||
| <37 | 3854 | 2135 (6.5) | 1719 (5.7) | ||
| 37–42 | 56 238 | 29 106 (89.2) | 27 132 (90.2) | ||
| ≥42 | 2035 | 1063 (3.3) | 972 (3.2) | ||
| Missing | 588 | 325 (1.0) | 263 (0.9) | ||
| Feeding patterns (<4 months) | 4.59 | 0.101 | |||
| Breast feeding | 30 716 | 15 925 (48.8) | 14 791 (49.2) | ||
| Formula feeding | 9959 | 5119 (15.7) | 4840 (16.1) | ||
| Mixed feeding | 21 612 | 11 363 (34.8) | 10 249 (34.1) | ||
| Missing | 428 | 222 (0.7) | 206 (0.7) | ||
| Normal delivery | 1.23 | 0.267 | |||
| Yes | 30 054 | 15 563 (47.7) | 14 491 (48.2) | ||
| No | 32 226 | 16 831 (51.6) | 15 395 (51.2) | ||
| Missing | 435 | 235 (0.7) | 200 (0.7) | ||
| One-child family | 34.94 | <0.001 | |||
| Yes | 43 207 | 22 748 (69.7) | 20 459 (68.0) | ||
| No | 15 665 | 7816 (24.0) | 7849 (21.6) | ||
| Missing | 3843 | 2065 (6.3) | 1778 (5.9) | ||
| Abortion | 3.16 | 0.076 | |||
| Yes | 14 849 | 7818 (24.0) | 7031 (23.4) | ||
| No | 47 401 | 24 561 (75.3) | 22 840 (75.9) | ||
| Missing | 465 | 250 (0.8) | 215 (0.7) | ||
| Asphyxia | 45.15 | <0.001 | |||
| Yes | 2146 | 1269 (3.9) | 877 (2.9) | ||
| No | 59 732 | 30 916 (94.8) | 28 816 (95.8) | ||
| Missing | 837 | 444 (1.4) | 393 (1.3) | ||
| Socioeconomic characteristics | |||||
| Area | 3.20 | 0.074 | |||
| Suburban | 49 231 | 25 709 (78.8) | 23 522 (78.2) | ||
| Urban | 13 371 | 6866 (21.0) | 6505 (21.6) | ||
| Missing | 113 | 54 (0.2) | 59 (0.2) | ||
| Income | 4.92 | 0.086 | |||
| Low | 16 762 | 8811 (27.0) | 7951 (26.4) | ||
| Middle | 34 442 | 17 898 (54.9) | 16 544 (55.0) | ||
| High | 10 279 | 5261 (16.1) | 5018 (16.7) | ||
| Missing | 1232 | 659 (2.0) | 573 (1.9) | ||
| Mother’s education level | 48.07 | <0.001 | |||
| Low | 17 541 | 9485 (29.1) | 8056 (26.8) | ||
| Middle | 24 365 | 12 435 (38.1) | 11 930 (39.7) | ||
| High | 16 972 | 8629 (26.4) | 8343 (27.7) | ||
| Missing | 3837 | 2080 (6.4) | 1757 (5.8) | ||
| Father’s education level | 33.79 | <0.001 | |||
| Low | 15 357 | 8280 (25.4) | 7077 (23.5) | ||
| Middle | 24 305 | 12 467 (38.2) | 11 838 (39.3) | ||
| High | 19 196 | 9805 (30.0) | 9391 (31.2) | ||
| Missing | 3857 | 2077 (6.4) | 1780 (5.9) | ||
The boldfaced number means P<0.05 for chi-square test.
BMI, body mass index.