Table 1 Demographic information for 12,771 participants

Gender

 Boy

235(59.8%)

3732(51.4%)

< 0.001

107(61.1%)

2556(51.6%)

0.013

 Girls

158(40.2%)

3522(48.6%)

68(38.9%)

2393(48.4%)

Age

 4 years old

21(5.4%)

183(2.5%)

< 0.001

1(0.6%)

16(0.3%)

0.004

 5 years old

33(8.4%)

241(3.3%)

3(1.7%)

20(0.4%)

 6 years old

32(8.1%)

277(3.8%)

4(2.3%)

30(0.6%)

 7 years old

52(13.2%)

715(9.9%)

18(10.3%)

420(8.5%)

 8 years old

43(10.9%)

544(7.5%)

29(16.6%)

591(11.9%)

 9 years old

53(13.5%)

1034(14.3%)

23(13.1%)

576(11.7%)

 10 years old

42(10.7%)

874(12.0%)

16(9.1%)

575(11.7%)

 11 years old

38(9.7%)

918(12.7%)

23(13.1%)

495(10.0%)

 12 years old

28(7.1%)

776(10.7%)

14(8%)

541(10.9%)

 13 years old

29(7.4%)

848(11.7%)

23(13.1%)

873(17.6%)

 14 years old

22(5.6%)

844(11.6%)

21(12%)

812(16.4%)

 Mean ± SD

8.87 ± 2.79

10.10 ± 2.67

< 0.001

10.18 ± 2.51

10.83 ± 2.39

< 0.001

Ethnicity

 Han Chinese

270(68.7%)

5878(81.0%)

< 0.001

174(99.4%)

4920(99.4%)

0.980

 Others

123(31.3%)

1376(19.0%)

1(0.6%)

29(0.6%)

BMI

 Underweight

5(1.3%)

49(0.7%)

0.418

4(2.3%)

33(0.6%)

0.017

 Normal weight

308(78.4%)

5589(77.0%)

126(72%)

3888(78.6%)

 Overweight

62(15.8%)

1291(17.8%)

34(19.4%)

835(16.9%)

 Obese

18(4.5%)

325(4.5%)

11(6.3%)

193(3.9%)

Parity

 First

254(64.6%)

4466(61.6%)

0.223

83(47.4%)

2315(46.8%)

0.865

 Others

139(35.4%)

2788(38.4%)

92(52.6%)

2634(53.2%)

Birth method

 Vaginal delivery

166(42.4%)

3395(46.8%)

0.077

106(60.6%)

2259(45.6%)

0.105

 Cesarean delivery

227(57.8%)

3859(53.2%)

69(39.4%)

2690(54.4%)

Gestational age at birth

 Full-term birth

363(92.4%)

6977(96.2%)

< 0.001

166(94.9%)

4764(96.3%)

0.339

 Others

30(7.6%)

277(3.8%)

9(5.1%)

185(3.7%)

Single birth

 Yes

385(97.8%)

7046(97.1%)

0.332

168(96.0%)

4706(95.1%)

0.583

 No

8(2.2%)

208(2.9%)

7(4.0%)

243(4.9%)

Birth weight (g)

 <2500

50(12.7%)

814(11.2%)

0.277

19(10.9%)

639(12.9%)

0.245

 2500–4000

337(85.8%)

6151(84.8%)

150(85.7%)

4016(81.2%)

 >4000

6(1.5%)

289(4.0%)

6(3.4%)

294(5.9%)