Vaginal examination vs. cervical length - which is superior in predicting preterm birth?
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.Design:
A retrospective case-control study.Setting:
Meir Medical Center, Kfar Saba, Israel.Population:
Women at 24-34 weeks of gestation who were hospitalized with PC and intact membranes.Methods:
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.Results:
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.Conclusions:
CL and BS have similar value in predicting PTB in patients with PC. For nulliparous women, CL is superior over the BS.