Background: To determine whether preterm delivery is more effectively predicted by sonographic cervical length measurement using fixed cut-off or gestational age-specific percentiles.
Methods: One hundred and eight patients hospitalized for suspected preterm labor (PTL) were studied prospectively between the 20th and the 33rd week of gestation.
Results: Cervical length below 15 mm, 25 mm and the 2.5th centile showed substantially equivalent odds ratios for delivery within 7 days (7.5, 7.6, and 7.1, respectively), while for delivery before the 34th week the odds ratios varied between 3.6 with cervical length <2.5rh centile and 6.2 with cervical length <25 mm. Moreover, the negative predictive value for delivery within 7 days exceeded 90% when cervical length was above 25 mm, the 10th and the 2.5th percentile, and 85% when above 15 mm.
Conclusion: The comparison of fixed and gestational age-specific cut-offs demonstrates a better reliability of fixed cut-offs (15 or 25 mm) in predicting preterm delivery, both before 34 weeks and within 7 days of the ultrasound examination.