Normative data of cervical length in singleton pregnancy in women attending a tertiary care hospital in eastern India

BACKGROUND & OBJECTIVES The length of cervix predicts the risk of preterm delivery. The objective of this study was to assess cervical length in pregnancy by transvaginal ultrasonography for generating normative data for nulliparous women at no special risk of preterm labour. METHODS An observational study was carried out in a tertiary care teaching hospital in eastern India in nulliparous women who delivered at term. A single sonologist assessed 224 women (once per subject) between 20 and 34 wk of gestation. Nulliparous women carrying a single foetus of confirmed gestational age were included; 216 subjects were finally considered for generation of normative data, excluding those delivering earlier than 37 or later than 42 wk. Other exclusion criteria were history of cerclage, any previous cervical surgery, smoking, or any medical disorder complicating pregnancy. RESULTS Cervix length at each week of gestation gradually decreased over the study period. Length at 20 and 34 wk was 40.5 ± 1.14 mm (mean ± SD) and 34.8 ± 1.34 mm respectively. The overall shortening over this 14 wk period was 5.7 mm, with 0.58 mm per week median rate of shortening. Pearson's correlation coefficient was -0.69 (95% CI -0.75 to -0.60; P< 0.001) for cervical length vis-à-vis gestational age. INTERPRETATION & CONCLUSIONS The serial normative data generated in our setting can be used to decide cut-off points for predicting risk of preterm labour in future studies. Validity of such prediction needs to be tested in larger cohorts of women assessed at specific gestational ages.