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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.