Table 5. Predictive ability of the final model.

PPV=Positive predictive value, NPV=Negative predictive value, AUC=Area under the receiver operating curve (ROC). The Past Live Birth subgroup contained only women with a past live birth where a previous preterm birth (PTB) would be a more useful predictor; this subgroup consisted of 1369 term birth (TB) and 96 PTB. The Nulliparous subgroup is women with no past live births; this subgroup consisted of 951 TB and 93 PTB. The Past Term Birth subgroup consists of women who have had a past live birth and have never had a PTB; this subgroup contained 1299 TB and 76 PTB.

	Entire Cohort (n=2509)			Past Live Birth Subgroup (n=1465)
	Past PTB	Model	Model (Spec>90%)	Past PTB	Model	Model (Spec>90%)
Prevalence	7.5	7.5	7.5	6.6	6.6	6.6
Sensitivity	10.6	17.5	31.2	20.8	26.0	35.4
Specificity	97.0	97.2	90.6	94.9	95.3	90.8
PPV	22.2	33.7	21.3	22.2	27.8	21.2
NPV	93.0	93.5	94.2	94.5	94.8	95.2
AUC	53.8	69.5	69.5	57.9	70.3	70.3

	Nulliparous Subgroup (n=1044)		Past Term Birth Subgroup (n=1375)
	Model (Spec>95%)	Model (Spec>90%)	Model (Spec>95%)	Model (Spec>90%)
Prevalence	8.9	8.9	5.5	5.5
Sensitivity	12.9	26.9	18.4	26.3
Specificity	96.6	90.9	96.5	91.2
PPV	27.3	22.3	23.3	14.9
NPV	91.9	92.7	95.3	95.5
AUC	65.7	65.7	65.9	65.9