Table 2 Logistic regression models in the prediction of preterm delivery within 14 days and before 34 weeksʼ gestation. In the first two models, either the first or the second cervical length measurement is used. In the third and fourth model the difference between both measurements is added to the first or second measurement.

	Delivery within 14 days		Delivery before 34 wks
	Estimate	p	Estimate	p
First cervical length
Constant	− 0.252	0.660	− 0.152	0.580
Cervical length	− 0.218	< 0.0001	0.247	< 0.0001
Second cervical length
Constant	− 0.708	0.156	− 0.115	0.790
Cervical length	− 0.141	< 0.0001	− 0.145	< 0.0001
First cervical length and difference between both measurements
Constant	− 1.169	0.002	− 0.325	0.517
Cervical length	− 0.120	0.001	− 0.132	< 0.0001
Difference	− 0.219	0.048	− 0.163	0.004
Second cervical length with difference between both measurements
Constant	− 1.157	0.053	− 0.220	0.680
Cervical length	− 0.121	0.002	− 0.025	< 0.0001
Difference	− 0.097	1.146	− 0.220	0.662