Table 1 Mother’s sociodemographic characteristics, prenatal care assistance, type of delivery and live birth at second pregnancy by preterm birth status at the first birth, 2001–2015 (n=1,764,025)

 Urban

1,303,734

77.07

1205,124

76.88

98,604

79.46

 Rural

387,896

29.93

362,396

23.12

25,493

20.54

 Missing

72,395

4.10

 No

1,015,851

62.24

946,688

62.60

69,163

57.67

 Yes

616,397

37.76

565,627

37.40

50,770

42.33

 Missing

131,777

7.47

 White

541,650

33.66

501,731

33.44

39,919

33.55

 Black/mixed-race

1,067,316

65,90

989,219

65.63

78,097

65.63

 Indigenous

10,552

0.65

9,564

0.64

988

0.83

 Missing

144,507

8.19

 < 8 years of study

638,901

36.78

592,159

36.80

46,742

36.56

 8 to 11 years of study

996,380

57.36

921,907

57.29

74,473

58.24

 ≥ 12 years of study

101,867

5.86

95,220

5.92

6647

5.20

 Missing

26,877

1.52

 Married, civil union

789,961

45.32

734,464

45.48

55,494

43.28

 Single, divorced, widow

953,095

54.68

880,365

54.52

72,729

56.72

 Missing

20.969

1.19

 None

30,255

1.73

27,210

1.68

3045

2.37

 1 to 3 visits

154,340

8.81

139,556

8.60

14,784

11.50

 ≥ 4 visits

1,566,330

89.46

1,455,636

89.72

110,694

86.13

 Missing

13,100

0.74

 <12 months

20,090

1.14

16,544

1.01

3,546

2.73

 12 to 23 months

297,459

16.86

266,622

16.31

30,837

23.76

 ≥24 months

1,446,476

82.00

1351,087

82.67

95,389

73.50

 Missing

0

0.0

 14 to 19 years

325,3112

18.44

290,336

17.77

34,976

26.95

 20 to 34 years

1,377,140

78.07

1,286,293

78.71

90,847

70.01

 35 to 49 years

61,573

3.49

57,624

3.53

3949

3.04

 Missing

0

0.0

 Vaginal

988,727

56.10

910,214

55.75

78,513

60.53

 Cesarean

773,562

43.90

722,428

44.25

51,134

39.44

 Missing

1,736

0.10

 Female

859,905

48.75

796,213

48.72

63,692

49.08

 Male

903,963

51.25

837,891

51.28

66,072

50.92

 Missing

157

0.01