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Table 1 Estimated mean probability ratios and 95% credible intervals of spontaneous labour, no anaesthesia, unassisted vaginal birth and no episiotomy

From: Factors promoting or inhibiting normal birth

  Probability Ratios
Spontaneous Labour No Anaesthesia Unassisted VB No Episiotomy
(N = 4611) (N = 2223) (N = 1636) (N = 1322)
M 95% CI M 95% CI M 95% CI M 95% CI
MATERNAL SOCIO-DEMOGRAPHIC CHARACTERISTICS
 Maternal age (+  5 years)a 0.94 0.91–0.98 0.90 0.82–0.98 0.99 0.97–1.00 0.96 0.87–1.00
 Completed secondary education 1.21 1.06–1.38 1.21 0.87–1.69 0.98 0.94–1.02 0.94 0.75–1.15
 Identifies as Aboriginal/Torres Strait Islander 1.01 0.70–1.33 0.94 0.56–2.31 0.91 0.69–1.00 0.80 0.27–1.08
Area of residence
 Major city 1.00   1.00   1.00   1.00  
 Inner regional 1.05 0.96–1.14 1.31 1.05–1.69 1.00 0.98–1.02 1.02 0.94–1.15
 Outer regional 1.06 0.97–1.16 1.75 1.33–2.44 1.00 0.97–1.02 1.05 0.98–1.22
 Remote/very remote 0.94 0.74–1.16 1.59 0.91–3.86 1.03 1.00–1.08 1.01 0.77–1.23
PREGNANCY DETAILS/COMPLICATIONS
Parity
 Multiparous – no previous CS 1.00   1.00   1.00   1.00  
 Multiparous – previous CS 0.38 0.32–0.45 0.64 0.50–0.82 0.55 0.28–0.81 0.72 0.32–0.98
 Primiparous 0.81 0.74–0.88 0.53 0.41–0.68 0.79 0.59–0.93 0.66 0.32–0.93
Multiple birth 0.47 0.28–0.70 0.50 0.32–0.87 0.06 0.00–0.56  
Pre-pregnancy BMI (+ 5 kg/m2)b 0.96 0.93–0.98 1.00 0.96–1.05 1.00 1.00–1.01 1.02 1.00–1.09
Gestational age (+  1 week)c 0.95 0.92–0.97 0.95 0.91–0.99 1.00 0.99–1.00 0.97 0.91–1.00
Gestational diabetes 0.70 0.59–0.82 0.94 0.70–1.35 0.97 0.90–1.01 1.03 0.87–1.25
High blood pressure 0.51 0.42–0.60 0.73 0.57–0.96 1.02 0.99–1.06 0.95 0.72–1.07
Low lying placenta 0.88 0.76–1.00 0.80 0.62–1.05 0.98 0.92–1.01 1.02 0.87–1.19
Other risk factors 0.76 0.69–0.82 1.15 0.97–1.40 1.00 0.97–1.01 1.00 0.91–1.08
ANTENATAL AND INTRAPARTUM CARE
Model of care
 Private obstetric care 1.00   1.00   1.00   1.00  
 Standard public care 1.40 1.29–1.54 1.35 1.07–1.77 1.00 0.97–1.02 1.09 1.01–1.83
 GP shared care 1.48 1.35–1.62 1.67 1.32–2.24 1.02 1.00–1.05 1.08 1.00–1.32
 Public midwifery continuity care 1.66 1.50–1.86 1.57 1.20–2.18 1.02 1.00–1.07 1.07 1.00–1.31
 Private midwifery care 1.93 1.64–2.25 3.35 0.96–109.68 1.03 0.98–1.09 1.14 1.01–1.58
Known care providers – labour/birth
 None of them 1.00   1.00   1.00   1.00  
 Some of them   0.76 0.63–0.91 0.95 0.87–0.98 0.96 0.83–1.03
 All of them   1.36 0.84–2.76 1.01 0.97–1.06 1.07 0.95–1.34
Continuity of care during labour/birth   1.45 1.21–1.78 1.02 1.00–1.05 1.03 0.98–1.16
Felt rushed/hurried during labour   1.19 0.92–1.60 0.94 0.84–0.99 1.09 1.00–1.38
LABOUR/BIRTH EXPERIENCE
Augmentation of labour
 Yes 1.00   1.00   1.00   1.00  
 No   2.72 2.15–3.56 1.01 0.99–1.03 1.05 1.00–1.19
 Not sure   1.31 0.85–2.36 0.93 0.78–1.00 0.91 0.52–1.12
Had continuous fetal monitoring   0.47 0.35–0.63 0.92 0.82–0.98 0.95 0.80–1.02
Freedom of movement throughout labour   1.54 1.20–2.01 1.02 1.00–1.06 1.08 0.99–1.35
Water immersion during labour   1.05 0.85–1.36 1.00 0.98–1.02 1.03 0.96–1.16
Birth outside business hours    1.01 0.99–1.03 1.01 0.93–1.10
Non-supine position during birth     1.11 1.01–1.41
  1. Note. M Mean probability ratio, CI Credible interval, CS Caesarean section, VB Vaginal birth
  2. aAge centred at 30 years
  3. bBMI centred at 28 kg/m2
  4. cCentred at 39 weeks gestation