Abstract Background:
Pre-term birth (PTB) has been a major problem leading to CNS damage and requires  expensive  and intensive care.To date, the gold screening tool  is cervical length (CL) measurement which has not been shown to be adequate as a single predictor of PTB. The aim of this investigation was to determine the predictive value of cervical consistency index (CCI) in low risk pregnancies.
 
Methods:
This was a prospective cross-sectional study performed on pregnant women at 14-28 weeks of gestation. The cervical length (CL) and anteroposterior cervical diameter were measured at rest (AP) and after at least 5 minutes gradual maximum compression (AP’) using the trans-vaginal probe and the CCI was calculated using this formula: CCI = (AP′ /AP)×100. The primary outcome was sPTB before 34+0w & 37+0w. Logistic regression and analysis of ROC curves were performed to evaluate the diagnostic power of CCI compared to CL.The inter-observer & intra-observer agreements were validated by ICC.
 
Results:
Among 110 participants with follow-up,11.7% leaded to PTB. Mean CCI for all subjects were 79.13%+/-10.3% that was lower in PTBs(58.2%). Pearson correlation coefficient was found to show a positive correlation between the weeks of pregnancy leading to delivery and the cervical length of women under study (P = 0.0001), and also show a positive correlation between GA in weeks and CCI in women (P = 0.013). According to ROC curve the best  cutoff was CCI= 68.82%, which had sensitivity of 68.8% and specificity =70.9% for prediction of PTB comparing with current cutoff CL<25mm which  had sensitivity= 34.8% & specificity =67.3%. The AUC for CCI for prediction of sPTB<37w was 0.863 while AUC for CL was 0.324.Inter-observer ICC for CCI and CL was 0.928 and 0.970 respectively while Intraobserver ICC was >0.90 for both.
 
Conclusion:
Among low risk women for PTB,CCI shows better diagnostic value than CL. This new variable appears to provide better prediction of sPTB than does CL.