Table 3 Unadjusted and adjusted risk ratios and 95Â % CI for OASIS among nulliparous and parous
|  | Nulliparous (n = 44 942) | Parous (n = 65 486) | ||
|---|---|---|---|---|
Unadjusted risk ratio | Adjusted risk ratio* | Unadjusted risk ratio | Adjusted risk ratio* | |
95Â % CI | 95Â % CI | 95Â % CI | 95Â % CI | |
Total | ||||
Sitting | 1.00 | 1.00 | 1.00 | 1.00 |
Lithotomy | 1.33 (1.21-1.46) | 1.17 (1.06-1.29) | 2.19 (1.83-2.62) | 1.66 (1.35-2.05) |
Lateral | 0.79 (0.69-0.91) | 0.79 (0.68-0.92) | 0.82 (0.67-1.01) | 0.84 (0.66-1.06) |
Knee | 0.88 (0.73-1.06) | 0.88 (0.71-1.09) | 0.78 (0.60-1.00) | 0.81 (0.58-1.11) |
Birth seat | 1.05 (0.92-1.21) | 1.05 (0.90-1.22) | 1.37 (1.07-1.74) | 1.36 (1.03-1.80) |
Supine | 0.89 (0.68-1.16) | 0.91 (0.67-1.22) | 0.84 (0.60-1.18) | 0.84 (0.55-1.30) |
Squatting | 0.81 (0.49-1.36) | 0.66 (0.36-1.24) | 1.79 (0.95-3.35) | 2.16 (1.15-4.07) |
Standing | 0.69 (0.36-1.33) | 0.71 (0.34-1.49) | 0.49 (0.20-1.18) | 0.40 (0.10-1.61) |
All four | 1.03 (0.59-1.78) | 1.12 (0.62-2.05) | 1.18 (0.53-2.64) | 0.95 (0.30-2.96) |
Maternal age (years) | ||||
 <35 | 1.00 | 1.00 | 1.00 | 1.00 |
 >35 | 1.25 (1.12-1.39) | 1.21 (1.08-1.36) | 1.13 (0.99-1.30) | 1.12 (0.96-1.32) |
Head circumference | ||||
 <35 | 1.00 | 1.00 | 1.00 | 1.00 |
 >35 | 1.76 (1.62-1.92) | 1.42 (1.29-1.57) | 1.95 (1.65-2.31) | 1.52 (1.23-1.88) |
Birth weight | ||||
 <4000 g | 1.00 | 1.00 | 1.00 | 1.00 |
 >4000 g | 2.16 (1.96-2.39) | 1.69 (1.52-1.88) | 2.54 (2.22-2.91) | 1.86 (1.57-2.21) |
Length of second stage | ||||
 <90 min | 1.00 | 1.00 | 1.00 | 1.00 |
 >90 min | 1.36 (1.25-1.47) | 1.15 (1.05-1.26) | 2.44 (1.98-3.01) | 1.93 (1.53-2.45) |
Length of gestation (weeks) | ||||
 <40 | 1.00 | 1.00 | 1.00 | 1.00 |
 >40 | 1.50 (1.38-1.64) | 1.20 (1.09-1.31) | 1.64 (1.42-1.87) | 1.25 (1.04-1.49) |
Epidural analgesia | ||||
 No | 1.00 | 1.00 | 1.00 | 1.00 |
 Yes | 1.02 (0.94-1.10) | 0.82 (0.74-0.90) | 1.28 (1.11-1.47) | 1.01 (0.88-1.24) |
Non-occiput anterior presentation | ||||
 No | 1.00 | 1.00 | 1.00 | 1.00 |
 Yes | 1.48 (1.20-1.82) | 1.30 (1.01-1.68) | 1.92 (1.47-2.51) | 1.51 (1.10-2.05) |
Oxytocin augmentation | ||||
 No | 1.00 | 1.00 | 1.00 | 1.00 |
 Yes | 1.31 (1.21-1.42) | 1.21 (1.09-1.35) | 1.33 (1.15-1.53) | 0.93 (0.78-1.12) |