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To determine whether cervical shortening between 22 and 27 weeks of gestation predicts spontaneous preterm delivery before 34 weeks better than a single cervical length (CL) measurement at 22 or 27 weeks in asymptomatic twins.
Prospective 13-center study over a 2-year-period re-analysed. CL was measured in 120 consecutive asymptomatic twin pregnancies during their routine ultrasound examination at 22 (21-23) and 27 (26-28) weeks. The results of these measurements were neither communicated to the patients nor used for their management. The area under the ROC curve was calculated for CL at 22 weeks, CL at 27 weeks, the percentage of cervical shortening between 22 and 27 weeks, and the cutoff point providing the best diagnostic performance, sensitivity and specificity for predicting spontaneous delivery <34 weeks was defined for each. Sensitivity, specificity, positive and negative likelihood ratios (LR+ and LR−) were then calculated with their 95% confidence intervals.
The study included 120 patients; four were excluded from the analysis because of medically indicated delivery before 34 weeks. Of the 116 women, 13 gave birth before 34 weeks (11.2%). The areas under the ROC curve were 0.67 for CL at 22 weeks, 0.75 for CL at 27 weeks, and 0.57 for the change in CL from 22 to 27 weeks. The three ROC curves obtained differed significantly at the 0.05 level (p-value= 0.027). Nonetheless, the ad hoc tests performed do not show a significant difference between the ROC curves compared pairwise. The best cutoff points were CL ≤35 mm at 22 weeks, CL ≤25 mm at 27 weeks, and cervical shortening of 20%. For equal sensitivity values (53.9%) for each, specificity for a CL ≤25 mm at 27 weeks was 87.5 (95% CI: 81-94), significantly better than for the other indicators.
The predictive performance of the cervical shortening does not differ from that of the measurement at either 22 or 27 weeks. However, because of its high specificity, CL ≤25 mm at 27 weeks appeared to be the most useful indicator for predicting preterm delivery before 34 weeks in this population.