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Table 2 Cox regression showing the hazard ratio (HR) of vaginal birth in the defined body mass index (BMI) groups, with and without adjustment for covariates

From: Maternal obesity and its effect on labour duration in nulliparous women: a retrospective observational cohort study

 

Total duration a

Covariates

Crude HR

95% CI

Adjusted HR

95% CI

BMI

 < 25

1

 

1

 

 25–29.9

0.83

[0.73–0.96]

1.01

[0.88–1.16]

 ≥ 30

0.94

[0.78–1.12]

1.07

[0.90–1.28]

Height

 < 160 cm

1

 

1

 

 160–169 cm

1.31

[1.08–1.59]

1.32

[1.09–1.61]

 170–179 cm

1.44

[1.18–1.76]

1.61

[1.32–1.98]

  ≥ 180 cm

1.66

[1.21–2.26]

1.73

[1.26–2.38]

Age

 < 25

1

 

1

 

 25–29

0.87

[0.77–0.99]

1.04

[0.91–1.19]

 30–34

0.82

[0.72–0.94]

0.97

[0.84–1.11]

 ≥ 35

0.62

[0.51–0.77]

0.68

[0.54–0.84]

Birthweight

 < 3.0 kg

1

 

1

 

 3.0–3.5 kg

0.77

[0.66–0.90]

0.66

[0.56–0.78]

 3.5–4.0 kg

0.53

[0.46–0.62]

0.49

[0.42–0.58]

 > 4.0 kg

0.38

[0.31–0.46]

0.38

[0.30–0.47]

Epidural

 No

1

 

1

 

 Yes

0.29

[0.26–0.32]

0.33

[0.29–0.37]

Augmentation with oxytocin:

 No

1

 

1

 

 Yes

0.31

[0.28–0.35]

0.40

[0.36–0.45]

Induced labour:

 No

1

 

1

 

 Yes

0.91

[0.82–1.02]

1.68

[1.48–1.90]

Phase 1

 

Crude HR

95% CI

Adjusted HR

95% CI

BMI

 < 25

1

 

1

 

 25–29.9

0.99

[0.86–1.14]

1.11

[0.96–1.28]

 ≥ 30

1.01

[0.85–1.21]

1.04

[0.86–1.24]

Phase 2

 

Crude HR

95% CI

Adjusted HR

95% CI

BMI

 < 25

1

 

1

 

 25–29.9

0.90

[0.96–1.28]

0.99

[0.86–1.14]

 ≥ 30

1.06

[0.96–1.28]

1.29

[1.07–1.55]

  1. Phase 1 was defined as the period of time from active labour until the cervix was fully dilated
  2. Phase 2 was defined as the period of time from when the cervix was fully dilated to the actual birth. Caesarean deliveries censored
  3. A hazard ratio (HR) >1 indicates an increased number of vaginal deliveries over time compared to the reference group; a shorter duration of labour. A HR < 1 indicates a decreased number of vaginal deliveries over time compared to the reference group; a longer duration of labour
  4. a77 women (4.1%) did not have duration measures recorded and were therefore not accounted for in analysis