TABLE 3.

Pooled estimates of pretest probabilities, likelihood ratios, and post-test probabilities for cervical length in the prediction of spontaneous preterm birth in women with twin pregnancies

Outcome	Cervical length cut-off (mm)	Pretest probability (%)	Likelihood ratios		Post-test probabilities (%)
			Positive test result	Negative test result	Positive test result	Negative test result
Asymptomatic women (testing at 20-24 weeks’ gestation)
Preterm birth <28 weeks	25	3.5	9.6	0.40	25.8	1.4
Preterm birth <32 weeks	20	6.8	10.1	0.64	42.4	4.5
Preterm birth <34 weeks	20	15.3	9.0	0.74	61.9	11.8
Preterm birth <37 weeks	25	41.2	4.4	0.83	75.5	36.8
Asymptomatic women (testing after 24 weeks’ gestation)
Preterm birth <32 weeks	25	6.1	2.7	0.47	14.9	3.0
Preterm birth <34 weeks	25	18.2	2.3	0.70	33.9	13.5
Preterm birth <37 weeks	25	53.6	1.8	0.75	67.5	46.4
Women with symptoms of threatened labor
Preterm birth <34 weeks	30	35.9	1.2	0.67	40.2	27.3
Preterm birth <37 weeks	25	67.2	1.9	0.69	79.6	58.6
	30	67.2	1.2	0.65	71.1	57.1