Predição do parto prematuro espontâneo em gestações gemelares pela medida do colo uterino: comparação entre medida obtida entre 18-21 semanas e 22-25 semanas de gestação e análise do encurtamento cervical / Prediction of spontaneous preterm birth in twin pregnancies by cervical length measurement: comparison between assessment at 18- 21 weeks and 22-25 weeks gestation and analyses of cervical shortening

Carolina Hofmeister de Andrade Mansú

OBJECTIVE: The aim of the present study is to compare the value of cervical assessment in twin pregnancies in predicting risk of spontaneous preterm delivery when performed at 18-21 weeks and 22-25 weeks gestation and to examine the value of cervical shortening observed between both periods. METHODS: This retrospective study involved 383 women carrying twins who were scheduled between 18-21 completed weeks (GROUP 1- 241 patients) and 22-25 completed weeks of gestation (GROUP 2- 266 patients). These two periods were assessed independently, and patients could be included in one or both with at least three weeks between the exams, whose delivery data was obtained. Patients included in both periods (GROUP 3- 124 patients) allowed the analysis of cervical shortening. Pregnancies presenting with the following complications where not included in the analyses: twin-twin transfusion syndrome, polihidramnius, fetal malformation, uterine patology; cases that underwent invasive procedures or uterine cerclage, premature delivery indicated for maternal or fetal complications and cases in which pregnancy outcome was impossible to obtain. Cervical length was the analyzed parameter. Area under the ROC curve was used to compare the predictive capacity of spontaneous preterm birth. To determine sensitivity, specificity, PPV and NPV, cervical length cut-off for short cervix was determined by Fujita et al (2002) curve, designed in our population. RESULTS: GROUP 1- The mean cervical length at 19.5 weeks (mean gestational age in the group) was 38.2 +- 8.7 mm. The rate of spontaneous preterm delivery (SPD) <28, <30, <32 and <34 weeks of gestation was 3.7%, 6.2%, 7.8% and 16.1%, respectively. The incidence of short cervix in the group was (14/241) 5.8%. Receiver operating characteristic curve analysis revealed area under the curve 0.64 (CI95% 0.53-0.75). Sensitivities of 33.3%, 33.3%, 30% and 23% and negative predictive values of 97.3%, 95.6%, 93.8% and 86.8% for delivery at <28, <30, <32, and <34 weeks gestation were achieved. GROUP 2- The mean cervical length at 23.3 weeks (mean gestational age in the group) was 35.6 +- 10.5 mm. The rate of SPD <28, <30, <32 and <34 weeks of gestation was 2.6%, 5.2%, 7.1% and 12.8%, respectively. The incidence of short cervix was (22/266) 8.2%. Receiver operating characteristic curve analysis revealed area under the curve 0.80 (CI95% 0.72-0.88), and this is larger than GROUP 1 area (p0,001). Sensitivities of 71.4%, 57.1%, 52.6% and 38.2% and negative predictive values of 99.1%, 97.5%, 96.3% and 91.4% for delivery at <28, <30, <32, and <34 weeks gestation were achieved. GROUP 3- Receiver operating characteristic curve analysis revealed area under the curve 0.81 (CI95% 0.73-0.89). The best cut-off for cervical shortening was reveled by the inflection point of the curve and was 2 mm/week. Sensitivities of 80%, 90%, 78.5% and 60.8% and negative predictive values of 98.9%, 98.9%, 96.8% and 90.6% for delivery at <28, <30, <32, and <34 weeks gestation were achieved. CONCLUSION: In twin gestations, assessment of cervical length at 22-25 weeks is better than __________________________________________________________________ assessment at 18-21 weeks to predict preterm delivery before 34 weeks. Cervical shortening of 6 mm/ 3weeks between 18 and 25 weeks gestation was a good predictor of spontaneous preterm birth in high risk population.

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