Ultrasound measurement of cervical length
Transvaginal ultrasound (TVUS) measurements of CL is consistently one of the strongest predictors of sPTB in women with symptoms of PTL and asymptomatic populations in both singletons and twins (Figure 30.2).
There is an increased likelihood of sPTB as the CL decreases. When using a short CL for risk prediction in an asymptomatic cohort, prediction is improved when screening a predefined high-risk population. For a 10% false-positive rate, the detection rate of spontaneous delivery before 32 weeks was 38% for maternal factors (obstetric history, smoking, etc.), 55% for CL measurement alone, and 69% for combined testing (35). A systematic review of TVUS measurement
Table 30.1 Effect of past obstetric history upon absolute risk of preterm birth
| First delivery | Second delivery | Absolute risk of preterm labour |
| Term singleton | Preterm singleton | 4.0% (95% CI 3.9-4.0) |
| Term twin | Preterm singleton | 1.3% (95% CI 0.7-2.0) |
| Preterm singleton | Preterm singleton | 20.2% (95% CI 19.9-20.6) |
| Preterm twin low prevalance of preterm labour between study populations affecting positive and negative predictive values despite stable sensitivities and specificities. In view of the multiple pathophysiology of PTB, it is unrealistic to expect a single biomarker to be able to predict sPTB in early gestation. The ideal biomarker test or predictive model should try to incorporate the fewest numbers of biomarkers to be measured, be highly sensitive and specific, exist in a biological fluid that is without risk to obtain, and be detectable early enough in pregnancy to allow for preventative measures to be taken.
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