. Author manuscript; available in PMC: 2015 Jan 1.

Published in final edited form as: Ultrasound Obstet Gynecol. 2014 Jan;43(1):48–53. doi: 10.1002/uog.13206

Table 2.

Results from the multivariable linear regression model evaluating the association between the gestational age at birth and independent variables.

All co-variates included			Selected co-variates
	Co-efficient (Std. Err)	p-value	Stepwise forward and backward (p<0.1) R²= 0.24; P<0.0001		Final included variables R²= 0.21; p<0.0001
Maternal demographics R² = 0.257; P<0.0001, F=9.98			Co-efficient (Std. Err)	p-value	Co-efficient (Std. Err)	p-value
Constant	184 (23)	<0.0001	196 (8.6)	<0.001	*195 (8.4)*	*<0.001*
Maternal age (years)	0.80 (0.26)	0.002	0.8 (0.25)	0.001	*0.72 (0.2)*	*0.003*
Gravidity	−2 (1.07)	0.06	− 2.02 (1)	0.06	-	-
History of prematurity	−14.6 (7)	0.036	−13 (6.8)	0.047	*−16.3 (6.8)*	*0.02*
BMI	−0.15 (0.2)	0.47	-	-	-	-
History of tobacco use	2.68 (4.5)	0.59	-	-	-	-
Gestational age at procedure	0.08 (0.1)	0.4	-	-	-	-
Fetal growth discordance	−0.056 (0.11)	0.62	-	-	-	-
Anterior placenta	−2.3 (3.2)	0.48	-	-	-	-
Stage 2	12.3 (6.2)	0.05	9.3 (3)	0.002	*7.4 (3)*	*0.02*
Stage 3	3.8 (6)	0.5	-	-	-	-
Stage 4	−0.37 (8.6)	0.97	-	-	-	-
Cervical length	0.35 (0.15)	0.02	0.36 (0.14)	0.008	*0.34 (0.14)*	*0.01*
Cerclage	−0.97 (9.1)	0.92	-	-	-	-
Center 2	17.7 (9.1)	0.05	-	-	-	-
Center 3	0.38 (9.4)	0.97	-	-	-	-
Cannula 10Fr	−12 (10)	0.23	-	-	-	-
Cannula 12Fr	−17 (7)	0.02	−14 (4.1)	0.001	*−10.7 (4)*	*0.01*
Amnioinfusion	−9.1 (4.3)	0.036	−10.8 (3.8)	0.004	*−13.1 (3.5)*	*<0.001*
Trocar entry (direct)	−4 (6.1)	0.5	-	-	-	-
Collagen plug	17.9 (5.8)	0.002	15.2 (4.7)	0.001	*11.4 (4.7)*	*0.02*
Solomon technique	6.9 (5.2)	0.19	-	-	-	-
iPPROM	−19.5 (3.2)	<0.0001	−18.9 (3.1)	<0.001	*−18 (3.1)*	*<0.0001*

Note: Stage 1, Center #1 and Cannula 9Fr were omitted in the regression due to collinearity with their respective co- categorical variables; iPPROM- iatrogenic preterm premature rupture of membranes, BMI- Body mass index (Kg/m²); Fr- French