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

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)