Table 1 Basic characteristics of participants

Maternal characteristics

 Pre-pregnancy BMI, mean (SD), kg/m²

22.34 (3.08)

21.54 (3.19)

22.65 (3.23)

0.01

21.88 (3.20)

21.61 (3.18)

0.51

21.52 (3.03)

 Maternal age, mean (SD), years

31.33 (3.32)

30.88 (3.51)

30.38 (3.56)

0.35

31.10 (4.12)

30.84 (3.47)

0.51

30.83 (3.52)

 HDP, N (%)

5 (11.1%)

75 (9.1%)

4 (5.6%)

0.43

7 (8.6%)

77 (8.9%)

0.48

84 (8.9%)

 Passive smoke, N (%)

12 (26.7%)

391 (47.3%)

32 (44.4%)

0.13

27 (33.3%)

406 (47.1%)

0.63

435 (46.1%)

 Drink during pregnancy, N (%)

5 (11.1%)

127 (15.4%)

7 (9.7%)

0.82

10 (12.3%)

129 (15.0%)

0.86

139 (14.7%)

 University background, N (%)

29 (64.4%)

690 (83.5%)

46 (63.9%)

0.51

51 (62.9%)

711 (82.5%)

0.41

765 (81.1%)

 Ethic Han, N (%)

41 (91.1%)

826 (100%)

70 (97.2%)

0.52

75 (92.6%)

862 (100.0%)

0.28

937 (99.4%)

 Income ≥ 100,000 yuan/year, N (%)

20 (44.4%)

459 (55.6%)

36 (50.0%)

0.29

35 (43.2%)

478 (55.4%)

0.66

515 (54.6%)

Children characteristics

 Birth height, mean (SD), cm

46.84 (1.89)

49.75 (1.23)

51.60 (1.81)

 < 0.001

47.95 (1.87)

49.89 (1.39)

 < 0.001

49.8 (1.50)

 BW, mean (SD), kg

2.19 (0.33)

3.31 (0.35)

4.23 (0.22)

 < 0.001

2.52 (0.48)

3.39 (0.42)

 < 0.001

3.33 (0.48)

BW groups, N (%)

 LBW

/

/

/

/

27 (33.3%)

18 (2.9%)

 < 0.001

45 (4.8%)

 NBW

54 (66.7%)

772 (89.6%)

 < 0.001

826 (87.6%)

 MBW

0 (0.0%)

72 (8.4%)

 < 0.001

72 (7.6%)

GA, mean (SD), weeks

35.55 (2.79)

39.21 ((1.41)

39.85 (0.79)

 < 0.001

34.92 (2.15)

39.43 (1.05)

 < 0.001

39.13 (1.51)

GA groups, N (%)

 Preterm

27 (60.0%)

54 (6.5%)

0 (0%)

 < 0.001

/

/

/

81 (8.6%)

 Term

18 (40.0%)

772 (93.5%)

72 (100%)

 < 0.001

862 (91.4%)

Gender, N (%)

 Boys

23 (51.1%)

479 (58.0%)

50 (69.4%)

0.01

32 (39.5%)

520 (54.1%)

0.13

552 (58.5%)

 Girls

22 (48.9%)

347 (42.0%)

22 (30.6%)

0.01

49 (60.5%)

342 (39.7%)

0.13

391 (41.5%)

Height at 4, mean (SD),cm

106.62 (4.33)

108.07 (4.81)

110.25 (4.62)

 < 0.001

107.91 (4.73)

107.24 (4.53)

0.71

107.26 (4.53)

Weight at 4, mean (SD), kg

16.99 (2.08)

17.75 (2.83)

19.30 (3.08)

 < 0.001

17.50 (2.66)

17.27 (2.60)

0.70

17.28 (2.56)

BMI at 4, mean (SD) kg/m²

14.93 (1.43)

15.13 (1.65)

15.83 (1.98)

0.002

14.98 (1.66)

14.97 (1.59)

0.25

14.97 (1.59)

Postnatal weight gain, mean (SD), kg

14.77 (2.15)

13.82 (2.42)

15.06 (3.01)

 < 0.001

15.18 (2.61)

13.86 (2.45)

 < 0.001

13.94 (2.48)