Maternal Body Mass Index and Risk of Obstetric Anal Sphincter Injury

Table 2

Risk factors for partial anal sphincter injury (𝑁=19923), total anal sphincter injury (𝑁=5456), and total anal sphincter injury involving the anal/rectal mucosa (𝑁=2500) among primiparous women with singleton vaginal cephalic births at term. OR for each variable studied in relation to anal sphincter injury was adjusted for all other variables and for year of delivery.

	Partial anal sphincter injury; ICD O70.2A%	Adjusted OR	95% CI	Total anal sphincter injury; ICD O70.2B%	Adjusted OR	95% CI	Total anal sphincter injuries involving the anal/rectal mucosa; ICD O70.3%	Adjusted OR	95% CI
Maternal body mass index
Unknown	4.4	0.99	0.94–1.04	1.2	0.89	0.81–0.96	0.5	0.92	0.80–1.04
Less than 18.5	4.1	1.24	1.14–1.36	1.4	1.48	1.27–1.74	0.6	1.42	1.12–1.81
18.5–24.9	4.4	1.00	Reference	1.3	1.00	Reference	0.6	1.00	Reference
25–29.9	4.4	0.92	0.88–0.95	1.3	0.90	0.84–0.97	0.6	0.95	0.88–1.05
30–34.9	4.3	0.90	0.84–0.96	1.1	0.77	0.67–0.88	0.5	0.78	0.64–0.94
35–39.9	3.9	0.79	0.70–0.90	1.0	0.65	0.50–0.83	0.5	0.79	0.56–1.12
40 or more	4.2	0.82	0.66–1.02	0.7	0.47	0.28–0.78	0.7	0.84	0.48–1.44
Maternal age, y
Younger than 20	1.3	0.32	0.28–0.36	0.5	0.46	0.38–0.57	0.2	0.44	0.32–0.59
20–24	2.8	0.64	0.61–0.68	0.9	0.68	0.63–0.74	0.4	0.67	0.60–0.75
25–29	4.6	1.00	Reference	1.3	1.00	Reference	0.6	1.00	Reference
30–34	5.5	1.16	1.13–1.20	1.5	1.07	1.00–1.14	0.7	1.01	0.92–1.11
35–39	5.5	1.14	1.09–1.21	1.4	0.96	0.86–1.06	0.6	0.84	0.71–0.98
40–44	5.1	1.02	0.89–1.16	1.0	0.73	0.55–0.96	0.4	0.56	0.36–0.80
45 or older	3.4	1.74	1.18–1.36	0.7	—	—	—	—	—
Fetal head position
Occipitoanterior position	4.3	1.00	Reference	1.2	1.00	Reference	0.6	1.00	Reference
Occipitoposterior position	6.8	1.27	1.18–1.36	2.5	1.60	1.43–1.79	1.1	1.56	1.32–1.84
Others	7.6	1.49	1.28–1.32	2.5	1.66	1.21–2.12	0.9	1.25	0.83–1.89
Instrumental delivery
No	3.3	1.00	Reference	0.9	1.00	Reference	0.4	1.00	Reference
Yes	9.5	2.62	2.58–2.70	2.0	2.93	2.78–3.10	1.4	2.92	2.70–3.16
Infant birth weight
Less than 3000	1.8	0.80	0.75–0.86	0.4	0.80	0.64–0.92	0.2	0.74	0.58–0.94
3000–3499	3.1	1.00	Reference	0.8	1.00	Reference	0.3	1.00	Reference
3500–3999	5.0	1.32	1.28–1.37	1.4	1.43	1.34–1.53	0.7	1.50	1.36–1.65
4000–4499	7.8	2.52	2.42–2.63	2.6	2.88	2.67–3.10	1.3	3.20	2.87–3.56
4500–4999	11.4	5.60	5.21–6.03	4.2	7.91	6.9–8.93	2.3	9.77	8.26–11.54
5000 or more	14.2	8.99	7.40–10.91	5.9	16.05	12.06–21.37	2.9	21.54	13.91–33.38