Prediction of patient‐specific risk of early preterm delivery using maternal history and sonographic measurement of cervical length: a population‐based prospective study

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Abstract
Objective: To develop a model for calculating the patient‐specific risk of spontaneous early preterm delivery by combining maternal factors and the transvaginal sonographic measurement of cervical length at 22 + 0 to 24 + 6 weeks, and to compare the detection rate of this method to that achieved from screening by cervical length or maternal characteristics alone.Methods: This was a population‐based prospective multicenter study involving 40 995 unselected women with singleton pregnancies attending for routine hospital antenatal care in London, UK. Complete follow‐up was obtained from 39 284 (95.8%) cases. The main outcomes were detection rate, false‐positive rate and accuracy of predicting spontaneous delivery before 32 weeks' gestation.Results: Spontaneous delivery before 32 weeks occurred in 235 (0.6%) cases. The detection rate of screening for early preterm delivery, at a fixed false‐positive rate of 10%, was 38% for maternal factors, 55% for cervical length and 69% for combined testing. There was good agreement between the model estimates and the observed probabilities of preterm delivery.Conclusions: This study provides a model that can give an accurate patient‐specific risk of preterm delivery. The detection rate of screening by a combination of maternal factors and the measurement of cervical length was substantially higher than that of screening by each method alone. Copyright © 2006 ISUOG. Published by John Wiley & Sons, Ltd.