Table 3. Unadjusted and Adjusted Relative Risk for the Probability of Cesarean Delivery.
| Unadjusted analysisa | Adjusted analysisa,b | |||||
|---|---|---|---|---|---|---|
| Relative Risk | Lower 95th% CI | Upper 95th% CI | Relative Risk | Lower95th %CI | Upper 95th% CI | |
| Total (kg/m2) | N=124,389 | N=101,961 | ||||
| BMI continuous (per 1 kg/m2) | 1.05 | 1.05 | 1.06 | 1.04 | 1.04 | 1.05 |
| BMI categories (per 1 stepc) | 1.37 | 1.35 | 1.38 | 1.31 | 1.29 | 1.32 |
| <25 reference | 1.0 | 1.0 | ||||
| 25.0-29.9 | 1.55 | 1.46 | 1.64 | 1.47 | 1.38 | 1.56 |
| 30.0-34.9 | 2.13 | 2.01 | 2.26 | 1.96 | 1.84 | 2.09 |
| 35.0-39.9 | 2.80 | 2.63 | 2.97 | 2.50 | 2.34 | 2.67 |
| > 40 | 3.75 | 3.53 | 3.99 | 3.06 | 2.86 | 3.29 |
| Nulliparas (kg/m2) | N=57,230 | N=47,427 | ||||
| BMI continuous (per 1 kg/m2) | 1.05 | 1.05 | 1.06 | 1.05 | 1.04 | 1.05 |
| BMI categories (per 1 stepc) | 1.38 | 1.36 | 1.39 | 1.32 | 1.30 | 1.34 |
| <25.0 reference | 1.0 | 1.0 | ||||
| 25.0-29.9 | 1.60 | 1.50 | 1.70 | 1.50 | 1.40 | 1.61 |
| 30.0-34.9 | 2.26 | 2.12 | 2.41 | 2.02 | 1.88 | 2.17 |
| 35.0-39.9 | 2.97 | 2.78 | 3.18 | 2.61 | 2.42 | 2.82 |
| > 40 | 3.86 | 3.60 | 4.14 | 3.19 | 2.95 | 3.45 |
| Prior Cesarean (kg/m2) | N=5,288 | N=4,122 | ||||
| BMI continuous (per 1 kg/m2) | 1.03 | 1.02 | 1.03 | 1.02 | 1.02 | 1.03 |
| BMI categories (per 1 stepc) | 1.18 | 1.15 | 1.22 | 1.13 | 1.10 | 1.17 |
| <25.0 reference | 1.0 | 1.0 | ||||
| 25.0-29.9 | 1.31 | 1.11 | 1.54 | 1.25 | 1.06 | 1.47 |
| 30.0-34.9 | 1.56 | 1.33 | 1.83 | 1.51 | 1.28 | 1.77 |
| 35.0-39.9 | 1.76 | 1.49 | 2.08 | 1.48 | 1.24 | 1.76 |
| > 40 | 2.12 | 1.79 | 2.51 | 1.82 | 1.52 | 2.19 |
| Multiparas w/o prior Cesareand (kg/m2) | N=61,871 | N=50,412 | ||||
| BMI continuous (per 1 kg/m2) | 1.07 | 1.06 | 1.07 | 1.05 | 1.04 | 1.05 |
| BMI categories (per 1 stepc) | 1.51 | 1.46 | 1.55 | 1.33 | 1.28 | 1.38 |
| <25.0 reference | 1.0 | 1.0 | ||||
| 25.0-29.9 | 1.51 | 1.29 | 1.77 | 1.34 | 1.12 | 1.59 |
| 30.0-34.9 | 2.43 | 2.08 | 2.84 | 1.84 | 1.54 | 2.19 |
| 35.0-39.9 | 3.57 | 3.03 | 4.20 | 2.51 | 2.08 | 3.02 |
| > 40 | 5.10 | 4.33 | 6.01 | 3.04 | 2.51 | 3.70 |
a
All p values < 0.001 when comparing each BMI level to the < 25.0 kg/m2 reference and when BMI considered continuous or as a grouped-category, with the exception in the Prior Cesarean and BMI 25.0-29.9 kg/m2 subgroup compared with the <25.0 kg/m2 reference where p=0.001 for unadjusted and p=0.007 for adjusted analysis.
b
Adjusted for site, maternal age, maternal height, maternal race, pre-gestational or gestational diabetes, cervical dilation at admission, and induction.
c
Per 1 step increase in BMI category (e.g., from < 25.0 to 25.0-29.9 kg/m2)
d
Includes cases with unknown prior cesarean status.
BMI body mass index
CI confidence interval