Skip to main content

Table 2 Adjusted hazard ratios of reproducing (HR) in relation to twinning, parental socio-demographic characteristics and birth characteristics by gender

From: Reproductive patterns among twins - a Swedish register study of men and women born 1973-1983

 

Females

Males

 

HRa

95% CI

HRb

95% CI

HRa

95% CI

HRb

95% CI

Twinbirth

0.89

0.86-0.93

0.91

0.88-0.95

0.92

(0.87-0.97)

0.96

0.91-1.01

Mother’s educational level

     

 9-10 years

Reference level

Reference level

 11-13 years

0.84

0.83-0.85

0.95

0.94-0.97

0.89

0.88-0-91

0.84

0.83-0.85

 ≥14 years

0.67

0.66-0.68

0.80

0.79-0.82

0.74

0.73-0.76

0.66

0.66-0.68

 Missing*

1.05

1.03-1.07

0.64

0.62-0.65

1.02

1.00-1.05

1.05

1.03-1.07

Father’s educational level

     

 9-10 years

Reference level

Reference level

 11-13 years

0.89

0.88-0.90

0.89

0.88-0.90

1.00

0.98-1.03

0.91

0.89-0.92

 ≥14 years

0.88

0.68-0.69

0.68

0.67-0.69

0.91

0.88-0.93

0.72

0.71-0.74

 Missing*

1.01

0.99-1.02

1.01

0.99-1.02

0.72

0.70-0.74

1.00

0.98-1.02

Mother’s civil status

     

 Divorced/widowed

Reference level

Reference level

 Married

0.81

0.79-0.83

0.81

0.79-0.83

0.88

0.85-0.91

0.88

0.85-0.91

 Unmarried

0.84

0.82-0.86

0.84

0.82-0.86

0.87

0.84-0.91

0.87

0.84-0.90

Parental country of origin

     

 One or both non-Nordic

Reference level

Reference level

 Both Nordic

1.34

1.32-1.37

1.34

1.32-1.37

1.20

1.17-1.23

1.20

1.17-1.23

Mother’s age at birth

     

 ≥34 years

Reference level

Reference level

 13-19 years

2.25

2.19-2.31

2.25

2.19-2.30

2.08

2.02-2.20

2.08

2.02-2.16

 20-26 years

1.59

1.56-1.62

1.58

1.55-1.61

1.56

1.52-1.60

1.55

1.52-1.59

 27-33 years

1.14

1.12-1.16

1.14

1.12-1.16

1.17

1.14-1.20

1.17

1.14-1.20

Mother’s parity

        

 Previous children

Reference level

Reference level

 No previous children

0.82

0.81-0.83

0.82

0.81-0.83

0.83

0.82-0.84

0.83

0.82-0.84

Year of birth $

1.03

1.03-1.03

1.03

1.03-1.03

0.94

0.94-0.94

0.94

0.94-0.94

Size for gestational age

       

 Appropriate for gestational age

Reference level

Reference level

 Small for gestational age

  

1.02

1.00-1.05

  

0.97

0.94-1.01

 Large for gestational age

  

1.02

0.99-1.05

  

1.03

0.99-1.07

Birthweight

        

 Normal birthweight (> = 2500 g)

Reference level

Reference level

 Low birthweight (1500–2499 g)

  

0.97

0.94-1.00

  

0.95

0.91-1.00

 Very low birthweight (<1500 g)

  

0.87

0.75-1.00

  

1.03

0.85-1.24

Gestational age

        

 Term (37–42 weeks)

Reference level

Reference level

 Preterm (32–36 weeks)

  

0.96

0.94-0.99

  

0.97

0.94-1.00

 Very preterm (<32 weeks)

  

0.88

0.78-0.99

  

0.78

0.68-0.90

 Post term (>42 weeks)

  

1.01

0.98-1.04

  

0.93

0.97-1.04

  1. *Parents with missing information on education were mainly immigrants and therefore included as a separate category in the analysis.
  2. $Included in the model as a continuous variable.
  3. aAdjusted for socio demographic variables presented in Table 1.
  4. bAdjusted for socio demographic and birth characteristics presented in Table 1.
Back to article page

BMC Pregnancy and Childbirth

ISSN: 1471-2393

Contact us