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Table 1 Factors associated with OASI recurrence at second vaginal birth, 2001–2011

From: The impact of first birth obstetric anal sphincter injury on the subsequent birth: a population-based linkage study

  OASI at 2nd birth No OASI at 2nd birth p Cr ORs Adj ORs with all risk factors in model
n = 276 n = 4532
(5.7%) (94.3%)
Country of birth* Asian 47 (17.0) 910 (20.2) 0.23 0.82 [0.60, 1.13] 0.89 (0.63, 1.26)
  Non Asian 226 (81.9) 3594 (79.3)   Reference Reference
FIRST BIRTH FACTORS       
  Diabetes Yes 17 (6.2) 174 (3.8) 0.06 1.64 [0.98, 2.75] 1.76 [1.03, 3.01]
   No 259 (39.8) 4358 (96.2)   Reference Reference
  Epidural/spinal/general Yes 109 (39.5) 1993 (44.0) 0.14 0.82 [0.64, 1.05] 0.79 [0.59, 1.06]
   No 167 (60.5) 2539 (56.0)   Reference Reference
  Birth mode Instrumental 120 (43.5) 2007 (44.3) 0.79 0.97 (0.76, 1.24) 1.04 [0.78, 1.40]
   Non Instrumental 156 (56.5) 2525 (55.7)   Reference Reference
  Episiotomy Yes 121 (43.8) 1939 (42.8) 0.73 1.04 [0.82, 1.33] 1.13 [0.86, 1.50]
   No 155 (56.2) 2593 (57.2)   Reference Reference
  Birthweight(kg) <3.0 29 (10.5) 462 (10.2) 0.34 1.08 [0.70, 1.66] 1.40 [0.89, 2.19]
   3.0 - <3.5 95 (34.4) 1636 (36.1)   Reference Reference
   3.5 - <4.0 119 (43.1) 1749 (38.6)   1.17 [0.89, 1.55] 0.94 [0.70, 1.27]
   ≥ 4.0 33 (12.0) 685 (15.1)   0.83 [0.55, 1.25] 0.53 [0.34, 0.82]
Inter pregnancy interval (years)* <1 50 (18.1) 1020 (22.5) 0.39 0.76 [0.52, 1.13] 0.78 [0.52, 1.17)
  1- < 2 126 (45.7) 1926 (42.5)   1.02 [0.74, 1.40] 1.04 [0.75, 1.45)
   2- < 3 59 (21.4) 919 (20.3)   Reference Reference
   ≥3 41 (14.9) 666 (14.7)   0.96 [0.64, 1.45] 1.01 [0.66, 1.54]
SECOND BIRTH FACTORS       
  Mat age <25 29 (10.5) 550 (12.1) 0.61 0.87 [0.58, 1.30] 0.93 [0.61, 1.41]
   25-34 189 (68.5) 3110 (68.6)   Reference Reference
   ≥35 58 (21.0) 872 (19.2)   1.09 [0.81, 1.48] 1.07 [0.78, 1.46]
  Hypertension Yes 16 (5.8) 161 (3.5) 0.05 1.67 [0.99, 2.84] 1.56 [0.90, 2.71]
   No 260 (94.2) 4371 (96.5)   Reference Reference
  Gestation (weeks)* <37 4 (1.5) 155 (3.4) <0.01 0.36 [0.13, 0.99] 0.73 [0.24, 2.19]
   37-38 29 (10.5) 840 (18.5)   0.49 [0.33, 0.73] 0.55 [0.36, 0.84]
   39-40 197 (71.4) 2779 (61.3)   Reference Reference
   ≥41 46 (16.7) 757 (16.7)   0.86 [0.62, 1.19] 0.72 [0.51, 1.02]
  Induction/Augmentation Yes 143 (51.8) 2428 (53.6) 0.57 0.93 [0.73,1.19] 0.95 [0.73, 1.24]
   No 133 (48.2) 2104 (46.3)   Reference Reference
  Epidural Yes 48 (17.4) 892 (19.7) 0.35 0.86 [0.62, 1.18] 0.95 [0.66, 1.38]
   No 228 (82.6) 3640 (80.3)   Reference Reference
  Birth mode Instrumental 24 (8.7) 289 (6.4) 0.13 1.40 (0.91, 2.16) 1.30 [0.80, 2.12]
   Non-instrumental 252 (91.3) 4243 (93.6)   Reference Reference
  Episiotomy Yes 68 (24.6) 1180 (26.0) 0.61 0.93 [0.70, 1.23] 0.84 [0.62, 1.14]
   No 208 (75.4) 3352 (74.0)   Reference Reference
  Infant sex* Male 158 (57.3) 2323 (51.3) 0.05 1.27 [1.00, 1.63] 1.12 [0.87, 1.44]
   Female 118 (42.7) 2208 (48.7)   Reference Reference
  Birthweight(kg)* <3.0 14 (5.1) 543 (12.0) <0.01 0.54 [0.30, 0.96] 0.56 [0.23, 1.06]
   3.0 - <3.5 80 (29.0) 1675 (37.0)   Reference Reference
   3.5 - <4.0 107 (38.8) 1653 (36.5)   1.36 [1.01, 1.83] 1.48 [1.08, 2.02]
   ≥4.0 75 (27.2) 658 (14.5)   2.39 [1.72, 3.31] 2.89 [1.98, 4.22]
  Year of second birth 01-05 68 (24.6) 1098 (24.2) 0.24 Reference Reference
   06-08 87 (31.5) 1643 (36.3)   0.86 [0.62, 1.19] 0.84 [0.60, 1.17]
   09-11 121 (43.8) 1791 (39.5)   1.09 [0.80, 1.48] 1.07 [0.78, 1.47]
  1. *Missing data <0.7%, these categories may not total 100%.
  2. Adjusted for all variables presented in table.