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Table 3 Adjusted Odds Ratios (OR) of obstetric anal sphincter injuries (OASIS) (n = 866/n = 189) among the primiparous (n = 73,813) and the multiparous women (n = 94,824) with vaginal delivery in University Hospitals between 1997 and 2007 in Finland.

From: Up to seven-fold inter-hospital differences in obstetric anal sphincter injury rates- A birth register-based study in Finland

CHARACTERISTICS/INTERVENTIONS Adjusted OR 95% CI p value
PRIMIPAROUS,
n = 73,813
   
Mode of delivery    
Vaginal spontaneous 1   
Vacuum assistance 2.65 2.29-3.06 ≤0.001
Epidural analgesia 0.73 0.62-0.86 ≤0.001
Augmentation with oxytocin 1.42 1.2-1.68 ≤0.001
Maternal age (year)    
≤19 1   
20-29 1.70 1.11-2.62 0.02
30-39 2.09 1.35-3.24 0.001
≥40 1.65 0.85-3.22 0.14
Birth weight (g)    
≤2,999 1   
3,000-3,499 1.4 1.44-2.62 ≤0.001
3,500-3,999 3.01 2.25-4.03 ≤0.001
≥4,000 4.97 3.67-6.74 ≤0.001
Hospital A 1   
Hospital B 1.37 1.08-1.74 0.01
Hospital C 1.52 1.21-1.91 ≤0.001
Hospital D 3.22 2.64-3.93 ≤0.001
Hospital E 1.11 0.81-1.52 0.53
MULTIPAROUS,
n = 94,824
   
Mode of delivery    
Vaginal spontaneous 1   
Vacuum assistance 2.23 1.32-3.76 0.003
Episiotomy 2.95 2.07-4.18 ≤0.001
Augmentation with oxytocin 1.36 1.00-1.84 0.05
Birth weight (g)    
≤2,999 1   
3,000-3,499 0.91 0.40-2.07 0.83
3,500-3,999 2.48 1.20-5.15 0.014
≥4,000 3.73 1.80-7.77 ≤0.001
Hospital A 1   
Hospital B 1.14 0.69-1.87 0.61
Hospital C 1.91 1.23-2.97 0.004
Hospital D 3.03 1.97-4.67 ≤0.001
Hospital E 1.0 0.53-1.92 0.99
  1. Odds ratios (OR) adjusted for mode of delivery, hospitals, induction, oxytocin, episiotomy, occiput posterior presentation (OP), epidural analgesia, spinal analgesia, use of nitrous oxide gas, paracervical block, maternal age, body mass index [BMI = body weight in kilograms/height in meters squared], length of active second stage of birth, birth weight, and head circumference. OP, spinal analgesia, BMI, length of active second stage of birth, and head circumference were adjusted for the years 2004-2007. All continuous variables (maternal age, BMI, birth weight, head circumference, and length of active 2nd stage of birth) were classified as categorical variables.