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Table 2 Association of first and second birth factors with planned caesarean section at second birth following OASI at first birth

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

   Planned CS Planned vaginal p crOR aOR
n = 1447 n = 4933
(22.7%) (77.3%)
Country of birth* Asian 202 (14.0) 979 (19.9) <0.01 0.66 (0.56, 0.77) 0.69 (0.58, 0.84)
  Non Asian 1236 (85.4) 3923 (79.5)    Reference
FIRST BIRTH FACTORS       
Diabetes Yes 70 (4.8) 200 (4.1) 0.19 1.20 (0.91, 1.59) 1.17 (0.84, 1.63)
  No 1377 (95.2) 4733 (95.9)    Reference
Hypertension Yes 133 (9.2) 430 (8.7) 0.58 1.06 (0.86, 1.30) 1.00 (0.79, 1.27)
  No 1314 (90.8) 4503 (91.3)    Reference
Gestation* (weeks) <37 34 (2.4) 84 (1.7) <0.01 1.49 (0.99, 2.23) 1.39 (0.87, 2.22)
  37-38 160 (11.1) 621 (12.6)   0.95 (0.78, 1.15) 0.81 (0.65, 0.99)
  39-40 782 (54.0) 2870 (58.2)   Reference Reference
  ≥41 471 (32.5) 1357 (27.5)   1.27 (1.12, 1.45) 1.42 (1.22, 1.65)
Induction/augmentation Yes 1064 (73.5) 3352 (68.0) <0.01 1.31 (1.15, 1.49) 1.11 (0.96, 1.30)
  No 383 (26.5) 1581 (32.0)    Reference
Epidural/spinal or GA Yes 915 (63.2) 2185 (44.3) <0.01 2.16 (1.92, 2.44) 1.73 (1.50, 2.00)
  No 532 (36.8) 2748 (55.7)    Reference
Birth mode Instrumental 815 (56.3) 2209 (44.8) <0.01 1.59 (1.41, 1.79) 1.16 (0.99, 1.35)
  Non-instr 632 (43.7) 2724 (55.2)    Reference
Episiotomy Yes 718 (49.6) 2121 (43.0) <0.01 1.31 (1.16, 1.47) 1.12 (0.98, 1.29)
  No 729 (50.4) 2812 (57.0)    Reference
OASIS Fourth 267 (18.5) 203 (4.1) <0.01 5.27 (4.35, 6.70) 4.95 (4.00, 6.13)
  Third/Unknown** 1180 (81.5) 4730 (95.9)    Reference
Birthweight (kg)* <3.0 130 (9.0) 504 (10.2) <0.01 1.10 (0.88, 1.37) 0.99 (0.77, 1.27)
  3.0- < 3.5 417 (28.8) 1772 (35.9)   Reference Reference
  3.5- < 4.0 562 (38.8) 1918 (38.9)   1.25 (1.08, 1.44) 1.22 (1.04, 1.43)
  ≥4.0 337 (23.3) 739 (15.0)   1.94 (1.64, 2.29) 1.66 (1.38, 2.01)
Interpregnancy interval <1 291 (20.1) 1094 (22.2) 0.04 0.91 (0.76, 1.09) 0.95 (0.77, 1.17)
(years) 1- < 2 601 (41.5) 2099 (42.6)   0.98 (0.84, 1.15) 1.03 (0.86, 1.22)
  2- < 3 292 (20.2) 999 (20.3)   Reference Reference
  ≥3 263 (18.2) 740 (15.0)   1.22 (1.00, 1.47) 1.13 (0.91, 1.40)
SECOND PREGNANCY       
Maternal age <25 136 (9.4) 593 (12.0) <0.01 0.80 (0.65, 0.97) 0.75 (0.60, 0.93)
  25-34 972 (67.2) 3381 (68.5)   Reference Reference
  35-40 309 (21.4) 897 (18.2)   1.20 (1.03, 1.39) 1.13 (0.96, 1.33)
  >40 30 (2.1) 62 (1.3)   1.68 (1.08, 2.62) 1.42 (0.87, 2.31)
Diabetes Yes 93 (6.4) 269 (5.5) 0.16 1.19 (0.93, 1.52) 0.99 (0.74, 1.33)
  No 1354 (93.6) 4664 (94.5    Reference
Hypertension Yes 53 (3.7) 187 (3.8) 0.82 0.97 (0.71, 1.32) 0.78 (0.55, 1.12)
  No 1394 (96.3) 4746 (96.2)    Reference
Gestation* (weeks) <37 85 (5.9) 168 (3.4) <0.01 2.03 (1.55, 2.67) 2.20 (1.64, 2.95)
  37-38 581 (4.02) 888 (18.0)   2.63 (2.31, 3.0) 2.87 (2.49, 3.31)
  39-40 757 (52.3) 3041 (61.7)   Reference Reference
  ≥41 24 (1.7) 835 (16.9)   0.12 (0.08, 0.18) 0.11 (0.07, 0.16)
Year of second birth 01-05 309 (21.4) 1194 (24.2) 0.03 Reference Reference
  06-08 515 (35.6) 1774 (36.0)   1.12 (0.96, 1.32) 1.06 (0.89, 1.27)
  09-11 623 (43.0) 1965 (39.8)   1.22 (1.05, 1.43) 1.19 (1.01, 1.42)
  1. *Missing data <0.7%, these categories may not total 100%.
  2. **Third/Unknown contains 107 records for which OASI was ascertained by procedure coding for 3rd/4th degree tear, and hence degree (3rd or 4th) of tearing is unknown.
  3. Adjusted for all variables presented in table.