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Table 4 Factors associated with spontaneous and iatrogenic preterm birth (<37 weeks) among singleton births, Nova Scotia, Canada, 1988 to 2003

From: Effects of socioeconomic position and clinical risk factors on spontaneous and iatrogenic preterm birth

Determinant

Spontaneous preterm birth

Iatrogenic preterm birth

Adjusted rate ratio

95% CI

P value

Adjusted rate ratio

95% CI

P value

Family income* < $4,430

0.99

0.85-1.15

0.92

1.12

0.77-1.62

0.56

 $4,430-$6,529

1.01

0.87-1.17

0.89

1.13

0.79-1.61

0.51

 $6,530-$11,914

0.95

0.84-1.07

0.42

0.99

0.74-1.32

0.94

 $11,915-$17,584

0.95

0.86-1.06

0.40

1.03

0.80-1.32

0.81

 $17,585-$24,949

1.07

0.97-1.19

0.16

1.00

0.79-1.26

0.97

 ≥$24,950

1.00

-

-

1.00

-

-

RSP (No)

1.09

1.00-1.18

0.05

1.02

0.84-1.23

0.84

Age <20 years

0.96

0.84-1.10

0.59

0.85

0.57-1.27

0.42

  20-24

1.00

-

-

1.00

-

-

  25-29

1.13

1.03-1.24

0.009

1.37

1.07-1.76

0.01

  30-34

1.34

1.21-1.49

<0.0001

1.46

1.11-1.92

0.007

  35-39

1.54

1.35-1.77

<0.0001

2.02

1.46-2.80

<0.0001

  ≥40

1.51

1.13-2.03

0.006

4.47

2.77-7.22

<0.0001

Parity 0

1.98

1.83-2.14

<0.0001

2.63

2.12-3.26

<0.0001

   1

1.00

-

-

1.00

-

-

   2

0.84

0.74-0.94

0.003

1.02

0.80-1.31

0.88

   ≥3

0.81

0.68-0.96

0.02

1.04

0.73-1.49

0.82

Marital status: Single

1.12

1.01-1.24

0.03

0.92

0.71-1.20

0.56

        Married

1.00

-

-

1.00

-

-

        Common law

1.17

1.05-1.30

0.006

0.95

0.72-1.26

0.74

        Other

1.25

0.96-1.63

0.09

1.30

0.75-2.23

0.35

Rural residence (Yes)

1.01

0.94-1.07

0.88

0.87

0.74-1.02

0.09

Weight <55 kg

1.33

1.22-1.45

<0.0001

0.97

0.78-1.21

0.80

   55-59

1.12

1.02-1.23

0.02

0.92

0.73-1.16

0.48

   60-69

1.00

-

-

1.00

-

-

   70-79

1.05

0.95-1.16

0.35

1.04

0.82-1.31

0.75

   80-89

1.07

0.94-1.22

0.33

0.91

0.67-1.22

0.52

   ≥90

1.15

1.01-1.31

0.04

1.21

0.92-1.60

0.17

Smoking: No

1.00

-

-

1.00

-

-

    Yes 1–9 cig.

1.29

1.15-1.44

<0.0001

1.22

0.92-1.63

0.17

    Yes ≥10 cig.

1.28

1.18-1.39

<0.0001

1.23

1.00-1.52

0.05

Prev. cesarean

0.83

0.73-0.94

0.003

4.91

3.96-6.08

<0.0001

Prev. low birth wt.

4.11

3.56-4.75

<0.0001

2.94

2.18-3.97

<0.0001

Prev. perinatal death

1.31

1.01-1.70

0.04

1.96

1.26-3.05

0.003

Period: 1988-1990

1.00

-

-

1.00

-

-

   1991-1993

1.00

0.91-1.10

0.98

1.09

0.85-1.40

0.49

   1994-1996

1.00

0.91-1.10

0.99

1.34

1.06-1.71

0.02

   1997-1999

1.15

1.04-1.26

0.005

1.35

1.06-1.72

0.01

   2000-2003

1.09

0.98-1.20

0.10

1.60

1.26-2.02

0.0001

  1. *Family income adjusted for family size and expressed in 1988 Canadian dollars. RSP denotes a Registered Saving Plan (see text).
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BMC Pregnancy and Childbirth

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