Table 1 Summary of the demographic and socioeconomic characteristics of participants. (Data from 2008 to 2018)

Maternal-based characteristics

 Age at delivery (year)

27.80

5.35

29.25

5.24

< 0.01

   < 25

3184

30.20

2278

17.84

  25–34

6037

57.26

8349

65.40

   ≥ 35

1322

12.54

2139

16.76

< 0.01

 Educational level

  Illiterate or primary school

1755

16.64

1519

11.90

  Secondary school

5003

47.45

4630

36.27

  High school or higher

3786

35.91

6617

51.83

< 0.01

 Residence

  Urban

4909

46.56

7087

55.51

  Rural

5635

53.44

5679

44.49

< 0.01

 Ethnicity

  Han

9082

86.18

11,101

86.96

  Other

1457

13.82

1665

13.04

0.08

 Parity

1.51

0.65

1.70

0.72

< 0.01

  1

5955

56.48

5311

41.60

   ≥ 2

4589

43.52

7455

58.40

< 0.01

 Annual household income

53,561.64

215,601.50

75,507.31

160,776.40

< 0.01

Healthcare-based characteristics

 Frequency of antenatal visit

6.37

3.71

8.95

4.41

< 0.01

   < 5

3182

30.21

1431

12.14

  5–7

3847

36.51

3003

25.47

   ≥ 8

3506

33.28

7358

62.40

< 0.01

 Mode of delivery

  Vaginal delivery

6149

58.37

6503

55.08

  Caesarean section

4385

41.63

5304

44.92

< 0.01

 Frequency of postnatal visit^a

1.27

1.34

1.26

1.11

< 0.01

  0

3695

35.49

3047

25.83

   ≥ 1

6715

64.51

8750

74.17

< 0.01

Infant-based characteristics

 Sex

  Male

5841

55.55

6355

53.82

  Female

4674

44.45

5452

46.18

0.01

 Birth weight (g)

3288.23

692.33

3375.29

839.74

< 0.01

   < 2500

464

4.43

544

4.61

  2500 ~ 4000

9411

89.88

10,273

87.08

   > 4000

596

5.69

980

8.31

< 0.01