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Table 2 Frequency and factors associated with incident and recurrent preterm birth in the second pregnancy, 2001–2015 (n = 1,764,025)

From: Differences in risk factors for incident and recurrent preterm birth: a population-based linkage of 3.5 million births from the CIDACS birth cohort

Second pregnancy variables

Incident preterm birth

Recurrent preterm birth

Pdifference b

n (%)

ORa

95% CI

n (%)

ORa

95% CI

Urban/rural area of residence

 Urban

86,747 (7.20)

Ref

Ref

18,003 (18.26)

Ref

Ref

0.96

 Rural

24,279 (6.70)

0.90

0.89–0.92

4395 (17.24)

0.90

0.87–0.94

 

Household overcrowding

 No

63,415 (6.70)

Ref

Ref

12,155 (17.57)

Ref

Ref

<0.00

 Yes

43,080 (7.62)

1.09

1.07–1.10

9469 (18.65)

1.01

0.98–1.04

 

Maternal race/ethnicity

 White

33,781 (6.73)

Ref

Ref

7237 (18.13)

Ref

Ref

<0.00

 Black/Mixed-race

71,741 (7.25)

1.04

1.03–1.06

14,003 (17.93)

0.95

0.92–0.98

 

 Indigenous

981 (10.26)

1.34

1.24–1.44

215 (21.76)

1.14

0.96–1.35

 

Maternal education

 ≥ 12 years of study

5659 (5.94)

Ref

Ref

1,060 (15.95)

Ref

Ref

0.27

 8 to 11 years of study

66,183 (7.18)

1.21

1.17–1.25

13,523 (18.16)

1.13

1.05–1.22

 

 <8 years of study

41,944 (7.08)

41,944 (7.08

1.12

1.09–1.16

8430 (18.04)

1.06

0.98–1.14

 

Marital status

 Married, civil union

53,922 (7.34)

Ref

Ref

10,132 (18.26)

Ref

Ref

<0.00

 Single, divorced, widow

60,422 (6.86)

0.85

0.84–0.86

12,948 (17.80)

0.90

0.87–0.93

 

Number of prenatal visits

 ≥ 4 visits

90,941 (6.25)

Ref

Ref

17,608 (15.91)

Ref

Ref

<0.00

 1 to 3 visits

19,606 (14.05)

2.44

2.40–2.49

4531 (30.65)

2.24

2.14–2.33

 

 None

3967 (14.58)

2.56

2.47–2.66

902 (29.62)

2.16

1.98–2.36

 

Interbirth interval

 ≥24 months

91,934 (6.80)

Ref

Ref

15,703 (16.46)

Ref

Ref

<0.00

 12 to 23 months

21,499 (8.06)

1.04

1.02–1.06

6366 (20.64)

1.22

1.17–1.26

 

 <12 months

2344 (14.17)

1.89

1.80–1.98

1293 (36.46)

2.58

2.38–2.79

 

Maternal age at birth

 20 to 34 years

86,081 (6.69)

Ref

Ref

15,415 (16.97)

Ref

Ref

<0.00

 14 to 19 years

24,548 (8.46)

1.16

1.14–1.18

7080 (20.24)

1.02

0.98–1.06

 

 35 to 49 years

5148 (8.93)

1.42

1.38–1.47

867 (21.95)

1.45

1.33–1.58

 

Type of delivery

 Vaginal

64,128 (7.05)

Ref

Ref

14,656 (18.67)

Ref

Ref

<0.00

 Cesarean

51,494 (7.13)

1.09

1.08–1.11

8679 (16.97)

0.96

0.92–0.99

 

Newborn sex

 Female

54,808 (6.88)

Ref

Ref

11,078 (17.39)

Ref

Ref

0.25

 Male

60,956 (7.27)

1.06

1.05–1.07

12,283 (18.59)

1.08

1.05–1.12

 
  1. aAnalysis adjusted for all model variables
  2. bPdifference represents the interaction between incident and recurrent preterm birth for the respective characteristic. The equation for this model is as follows: Logit [ Pr (PTB2=1/Risk factors)] = β0 + β1 (PTB1) + β2 (risk factor X2) + β3 (PTB1) × (risk factor X2), where PTB1 and PTB2 are indicators of a preterm birth in the first and second pregnancy, respectively. Risk factor X2 is a risk factor in the second pregnancy. The model shows a single risk factor, but additional risk factors were added by including additional terms for each risk factor and its interaction with the first pregnancies’ preterm delivery status, PTB1
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BMC Medicine

ISSN: 1741-7015

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