Table 2 Incidence of OASI in subgroups in vaginal deliveries

4384

142

3.2

5999

53

0.9**

10,383

195

1.9

Maternal age at birth a) (years)

– 19

49

0

0

–

2

0

0

–

51

0

0

–

20 – 24

816

16

2

1.0

263

0

0

–

1079

16

1.5

1.0

25 – 29

2056

68

3.3

1.69 (0.9-2.9)

1701

10

0.6

1.0

3757

78

2.1

RR 1.4 (0.8-2.4)

30 – 34

1011

38

3.8*

1.92 (1.1-3.4)

2541

28

1.1

1.87 (0.9-3.8)

3552

66

1.9

RR 1.25 (0.7-2.2)

35 – 39

237

7

3.0

1.51 (0.6-3.6)

1062

12

1.1

1.9 (0.8-4.2)

1299

19

1.5

RR 0.99 (0.5-1.9)

40 –

49

0

0

205

1

0.5

254

1

0.4

–

Sectio antea

No

–

–

–

5465

27

0.5

1.0

–

–

–

Yes

–

–

–

534

26

4.9**

9.8 (5.7-16.7)

–

–

–

Gestational age (days)

<  266

400

1

0.3

0

399

1

0.3

–

799

2

0.3

–

266 – 272

504

11

2.2

1.0

615

4

0.7

1.0

1119

15

1.3

1.0

273 – 279

912

29

3.2

1.46 (0.7-2.9)

1260

10

0.8

1.22 (0.4-3.9)

2172

39

1.8

RR 1.34 (0.7-2.4)

280 – 286

1334

44

3.3

1.51 (0.8-2.9)

2154

22

1.0

1.57 (0.5-4.5)

3488

66

1.9

RR 1.41 (0.8-2.5)

≥ 287

1234

57

4.6*

2.12 (1.1-4)

1571

16

1.0

1.57 (0.5-4.7)

2805

73

2.6*

RR 1.94 (1.1-3.4)

Dystocia

No

3680

115

3.1

1.0

5673

44

0.8

1.0

9353

159

1.7

1.0

Yes

704

27

3.8

1.19 (0.8-1.7)

326

9

2.8*

3.19 (1.7-5.8)

1030

36

3.5**

RR 2.06 (1.4-2.9)

Epidural a)

No

2984

94

3.1

1.0

5046

38

0.8

1.0

8030

132

1.6

1.0

Yes

1352

47

3.5

1.07 (0.8-1.4)

701

15

2.1**

2.35 (1.52-3.6)

2053

62

3.0**

RR 1.86 (1.4-2.5)

Mode of delivery

SVD

3835

89

2.3

1.0

5863

40

0.7

1.0

9698

129

1.3

1.0

OVD

549

53

9.7**

3.19 (2.5-4)

136

13

9.6**

11.9 (7.2-19.6)

685

66

9.6**

RR 7.2 (5.4-9.6)

Episiotomy

No

4186

129

3.1

1.0

5945

52

0.9

1.0

10,130

181

1.8

1.0

Yes

198

13

6.6**

2.1 (1.2-3.6)

55

1

1.8

2.08 (0.3-14.7)

253

14

5.5**

RR 3.06 (1.8-5.2)

Birth position a)

Recumbent

601

23

3.8

801

7

0.9

1401

30

2.1

Semi-recumbent

1272

41

3.2

1468

16

1.1

2740

57

2.1

Sitting upright/birth chair

11

0

0

17

0

0

28

0

0

Squatting

6

0

0

9

0

0

15

0

0

Standing

28

4

14.3*

70

0

0

98

4

4.1

All fours

47

2

4.3

96

1

1.0

143

3

2.1

Side lying

157

4

2.5

366

3

0.8

523

7

1.3

Water birth

144

5

3.5

303

1

0.3

447

6

1.3

Sub-total

2266

79

3.5

3130

28

0.9

5395

107

2.0

Birth weight (grams)

– 2999

820

19

2.3

1.0

730

4

0.5

1.0

1550

23

1.5

1.0

3000 – 3499

1489

25

1.7

0.73 (0.4-1.3)

1636

10

0.6

1.12 (0.4-3.5)

3125

35

1.1

0.75 (0.4-1.3)

3500 – 3999

1481

66

4.5*

1.92 (1.2-3.2)

2211

17

0.8

1.54 (0.5-4.6)

3692

83

2.2

1.52 (0.96-2.4)

4000 –

594

32

5.4**

2.33 (1.3-4.1)

1422

22

1.5*

2.82 (0.98-8.2)

2016

54

2.7*

1.81 (1.1-2.9)