The use of cervical length and change in cervical length for prediction of spontaneous preterm birth in asymptomatic twin pregnancies

ObjectiveTo assess the association between cervical length (CL) and change of CL over two measurements and preterm birth (PTB) at <32 weeks in asymptomatic twin pregnancies.Study designThis study was undertaken in the multiple pregnancy antenatal clinic at the Security Forces Hospital (SFH), a tertiary care hospital in Riyadh, Saudi Arabia, between November 2005 and October 2010. This study involved 420 women with asymptomatic twin gestations, but only 209 unselected patients completed the study and met the inclusion criteria. All patients had a CL measurement by transvaginal ultrasound at 20–23 weeks, and a second CL measurement was done within 3–5 weeks of the initial measurement. Patients were classified into two groups, group A with significant shortening of CL, and group B without significant shortening of CL. Comparisons between the groups were performed using a chi-square test or a Fisher exact test for categorical variables, whereas Student's t-test or Wilcoxon's rank-sum test was used for continuous variables. We employed ROC curves to compare the diagnostic accuracy of actual cervical length and percent change in cervical length in predicting preterm birth events. All analyses were performed using the SAS/STAT software.ResultsThere were 35 (16.7%) patients whose CL shortened by ≥25% (group A), and 174 (83.3%) whose CLs either did not shorten or shortened by <25% (group B). Preterm birth at <28, <30, <32, and <34 weeks gestation was higher in group A than in group B even if the CL was >25 mm. The use of CL shortening was superior, but not statistically significantly, to the use of CL for the prediction of PTB at <32 (P = 0.0524) and <34 weeks (P = 0.281), but CL was preferred for the prediction of PTB at <28 (P = 0.037) and <30 weeks (P = 0.0457).ConclusionThe test of two CL measurements, the first between 20 and 23 weeks gestation and another CL measurement 3–5 weeks later, with a difference of ≥25%, is a good predictor for preterm birth in asymptomatic twin pregnancies, even if the CL is >25 mm.