Normative Values of Mid Trimester Cervical Consistency Index in Women Delivering at Term

Cervical Consistency Index (CCI) is a new technique to measure the consistency of Cervix (softening) and is expected to show changes before cervical shortening. The aim of this study was 1. To find out the normative values of mid-trimester Cervical Consistency Index in women delivering at term. 2. To compare the discriminative ability of cervical consistency index with cervical length for prediction of spontaneous preterm birth. A total of 144 antenatal patients undergoing mid-trimester anomaly scan were subjected to transvaginal cervical length measurement as per Fetal Medicine Foundation criteria. Cervical consistency index was measured as defined by Para et al. The anterior–posterior diameter of cervix was measured before compression (AP) and after compression (AP') in the same sitting. Cervical consistency index (CCI) was calculated by the formula: $${\text{CCI }} = {\text{AP}}^{\prime } /{\text{AP}} \times {1}00.$$ The result of CCI was not used in the clinical management of the patient. Women who delivered at 37 weeks and beyond were included to form the normative data. An attempt was made to study the ability of mid-trimester cervical consistency index to predict spontaneous preterm birth as compared to cervical length (CL). Range of CCI in our study was 41–100% and that of CL was 2–4 cm.Based on values of CCI and CL an ROC curve was made, AUC measured for CCI was 0.923 and for CL was 0.849. The cut off determined for CCI was 64.5%, above which all women delivered at  ≥ 37 weeks. Only Two women who delivered preterm (< 37) weeks had a CCI of less than 64.5% (64 and 47%), but cervical length was greater than 2.5 cms in both of them. The Sensitivity, Specificity, Positive Predictive Value, Negative Predictive Value and accuracy of CCI for predicting term delivery at a cutoff of 64.5% in our study was 83.8%, 100%, 100%, 8% and 93.8% respectively, whereas the corresponding figures for predicting preterm delivery were 100%, 83.8%, 8%, 100% and 93.8%. Discriminative ability of CCI in comparison to CL could not be determined because only two women delivered preterm in our study. This was a pilot study to form the normative values of CCI for women delivering at term. At a cutoff value of 64.5% or more all women delivered at term. Two women who delivered preterm had a CCI of less than 64.5%. Further large studies are required before CCI can be incorporated as a routine to assess the antenatal cervix.