Table 2 Cox’s proportional hazards regression model for estimating risk of cesarean section*

 Trans-labial ultrasound plus vaginal examination

–

–

–

1.0 (ref.)

–

 Vaginal examination only

2.16

0.598

13.01

8.65

< 0.001

 Age

0.061

0.035

2.954

1.065

0.086

 Mother’s current weight

0.031

0.053

0.330

0.970

0.566

 BMI

0.075

0.143

0.271

1.077

0.603

 Gestational age

0.078

0.279

0.078

0.925

0.779

 Frequency of pregnancy

0.676

0.269

6.327

0.509

0.012

 Weight at birth

0.002

0.001

5.846

0.998

0.016

 OA

–

–

–

1.0 (ref.)

–

 OP

1.39

0.696

4.04

4.053

0.034