Maternal Body Mass Index and Risk of Obstetric Anal Sphincter Injury
Table 3
The effect of fetal head position at delivery and the effect of instrumental delivery on the risk for any anal sphincter injury according to maternal body mass index among primiparous women with singleton vaginal cephalic births at term.
Maternal BMI
Occiput posterior
Occiput anterior
OR*
95% CI
Instrumental vaginal delivery
Spontaneous vaginal delivery
OR**
95% CI
No anal sphincter injury ()
Anal sphincter injury ()
No anal sphincter injury ()
Anal sphincter injury ()
No anal sphincter injury ()
Anal sphincter injury ()
No anal sphincter injury ()
Anal sphincter injury ()
Unknown
1583
3140
48720
3140
1.23
1.04–1.46
2106
1245
42601
2106
2.70
2.50–2.91
Less than 18.5
361
32
11775
743
1.21
0.81–1.80
482
302
10410
482
3.12
2.68–3.14
18.5–24.9
8037
959
250460
16099
1.44
1.34–1.55
10949
6302
220189
10949
2.71
2.62–2.80
25–29.9
2972
213
79157
5221
1.19
1.05–1.35
3419
2123
68964
3419
2.78
2.62–2.94
30–34.9
774
96
21853
1336
1.62
1.28–2.05
875
568
19208
875
3.15
2.81–3.54
35–39.9
210
19
6165
351
1.27
0.77–2.09
259
112
5367
259
2.02
1.58–2.58
40 or more
70
0
1954
114
—
—
80
43
1700
80
2.21
1.46–3.06
Adjustments were made for year of birth, maternal age, birth weight, and instrumental delivery. **Adjustments were made for year of birth, maternal age, birth weight, and fetal head position.
