Vaginal examination vs. cervical length - which is superior in predicting preterm birth?

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To compare the predictive value of preterm birth (PTB) by transvaginal sonographic cervical length (CL) measurement to digital examination of the cervix (Bishop score - BS), in patients with premature contractions (PC) and intact membranes.


A retrospective case-control study.


Meir Medical Center, Kfar Saba, Israel.


Women at 24-34 weeks of gestation who were hospitalized with PC and intact membranes.


All patients underwent CL and BS measurements upon admission. Power analysis revealed that 375 patients were needed to show a significant difference between the two methods for predicting PTB. Each one served as her own control.

Main outcome measures:

PTB<37 and<34 weeks.


Receiver-operator characteristic curve (ROC) and logistic regression analyses indicated a correlation between both shortened CL and increased BS to PTB (P<0.001). Neither test offered an advantage in predicting PTB. Areas under the curve for BS and CL ROC were similar for PTB before 37 weeks gestation (0.611 vs. 0.640, P=0.28). For nulliparous women, CL predicted PTB better that BS (0.642 vs. 0.724, P=0.03). For singleton and multiple pregnancy pregnancies, BS and CL did not differ significantly in predicting PTB (P=0.9, P=0.2, respectively). For nulliparous with multiple pregnancy, the BS and CL ROC curves differ nearly significantly (0.554 vs. 0.709, P=0.07), with better predictive ability for CL.


CL and BS have similar value in predicting PTB in patients with PC. For nulliparous women, CL is superior over the BS.

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