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Does Second-Trimester Cervical Length Predict Prolonged Pregnancy?

INTRODUCTION: Third-trimester cervical length has been correlated with delivery timing. Given that second-trimester ultrasonography is routine practice, we sought to evaluate whether second-trimester cervical length is associated with prolonged pregnancy. METHODS: We performed a secondary analysis of data involving women with singleton gestations between 18 0/7 and 23 6/7 weeks of gestation undergoing universal transvaginal ultrasound cervical length screening for preterm birth prediction from January 1, 2012, to December 30, 2012. Women with prior spontaneous preterm births, cerclage in situ, and deliveries at outside institutions were excluded. Women were included if they had spontaneous labor, rupture of membranes, or reached 41 weeks of gestation. The primary outcome was the incidence of prolonged pregnancy (41 0/7 weeks of gestation and beyond). A receiver operating characteristic curve was calculated to identify the threshold cervical length predictive of a prolonged pregnancy. Statistical analysis was performed using SPSS 20.0. RESULTS: Of the 660 women who met inclusion criteria, 108 (16.4%) had prolonged pregnancies. Women with prolonged pregnancies had a higher mean body mass index and were less likely to have had a prior vaginal delivery compared with women without prolonged pregnancies. Women with prolonged pregnancies also had higher mean cervical length (43 compared with 42 mm, P=.057) and a higher incidence of cervical length greater than 30 mm (100% compared with 96%, P=.035; Table 1). The receiver operating characteristic curve demonstrated an area under the curve of 0.542 (standard error 0.027; Figure 1); no optimal cervical length was predictive of a prolonged pregnancy. Table 1 Second-Trimester Cervical Length in Women With Prolonged Pregnancies: Demographic and Cervical Length Data Fig. 1. Receiver operating characteristic curve of second-trimester cervical length for prolonged pregnancy. CONCLUSIONS: Second-trimester cervical length is not predictive of prolonged pregnancy.