Cervical length as a predictor of preterm delivery: Gestational age-related percentiles vs fixed cut-offs

Department of Gynecology, Obstetrics and Neonatology, University of Parma, Parma, Italy.
Acta bio-medica: Atenei Parmensis 01/2008; 78(3):220-4.
Source: PubMed


To determine whether preterm delivery is more effectively predicted by sonographic cervical length measurement using fixed cut-off or gestational age-specific percentiles.
One hundred and eight patients hospitalized for suspected preterm labor (PTL) were studied prospectively between the 20th and the 33rd week of gestation.
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.
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.

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    • "Transvaginal ultrasound measurements of cervical length have been used to identify cervical remodeling (Crane and Hutchens, 2008; Chiossi et al., 2006; Gomez et al., 2005; Gramellini et al., 2007; Hassan et al., 2000, 2006; Iams et al. 1996; Iams, 2003; Newman et al., 2008; Schmitz et al., 2008). Although ultrasound measurements of cervical structure (length and funneling) are useful for determining the risk of preterm delivery (Gomez et al., 1994, 2005; Honest et al. 2003), these measurements alone have low positive predictive value (Gramellini et al., 2007; Iams, 2003) and in many cases did not outperform the Bishop score in predicting preterm birth (Newman et al., 2008; Schmitz et al., 2008). There is a need to develop techniques that detect tissue remodeling in the pregnant cervix before effacement and dilation occur. "
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    ABSTRACT: Dysregulated remodeling of the cervix precedes preterm birth, a major cause of infant mortality and morbidity. The goal of this work was to identify changes in the mechanical properties of the cervix in late gestation. The tensile and load relaxation properties of cervices from rats 15-21 days (full term) post-conception were measured. Stiffness and load at 25% circumferential strain decreased with gestational age and correlated with the initial circumference of the cervix. Load-relaxation curves were accurately described by a seven parameter quasi-linear viscoelastic model, where three parameters associated with stiffness and load capacity decrease with gestational age and correlate with initial circumference. Time-dependent parameters did not depend on age or structure. Mechanical properties correlated with water content, but unexpectedly not with measures of collagen content, solubility, or organization. Quantitative measurements of cervical stiffness and structure will lead to a more accurate description of cervical remodeling and prediction of preterm birth.
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    ABSTRACT: To assess the predictive performance of cervical length measurement at presentation and 24h later in women with symptoms of preterm labour. Cervical length was measured transvaginally at presentation and 24 hours later in 122 women presenting with threatened preterm labour between 23 and 33+6 gestational weeks. Six women delivered within 1 week of presentation. The sensitivity and specificity of a cervical length <15 mm at admission for delivery within one week was 83.3 and 95.8%, respectively. A reduction of >20% in cervical length 24h after admission predicted 50% of preterm deliveries within 1 week, with a specificity of 92.7%; in combination with cervical length at presentation it did not improve the prediction. The same was observed for birth before 32 weeks (N=9) and birth before 35 weeks (N=15). Women with threatened preterm labour and a cervical length of <15 mm at presentation are at high risk of delivering preterm. Cervical change in the following 24 hours does not seem to improve the prediction.
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    ABSTRACT: To integrate data on the performance of cervical length measurement for the prediction of preterm birth in symptomatic women. MEDLINE, SCOPUS and manual searches for studies with transvaginal ultrasound measurement of the cervical length in symptomatic women were carried out. Random effects models were used for data integration, and pooled test estimates of sensitivity, specificity, and positive and negative likelihood ratios (LR+ and LR-) were calculated along with their 95% CIs. Twenty-eight studies fulfilled the selection criteria. For birth within 1 week from presentation, the pooled sensitivity, specificity, LR+ and LR- of cervical length < 15 mm were 59.9% (95% CI, 52.7-66.8%), 90.5% (95% CI, 89.0-91.9%), 5.71 (95% CI, 3.77-8.65) and 0.51 (95% CI, 0.33-0.80), respectively. The same estimates for studies with presentation at or before 34 + 0 weeks were 71.0% (95% CI, 60.6-79.9%), 89.8% (95% CI, 87.4-91.9%), 5.19 (95% CI, 2.29-11.74) and 0.38 (95% CI, 0.11-1.34), respectively. For prediction of birth before 34 weeks, the pooled sensitivity, specificity, LR+ and LR- of cervical length < 15 mm were 46.2% (95% CI, 34.8-57.8%), 93.7% (95% CI, 90.7-96.0%), 4.31 (95% CI, 2.73-6.82) and 0.63 (95% CI, 0.38-1.04), respectively. There was considerable heterogeneity across studies in most estimates. Measurement of cervical length in symptomatic women can detect a significant proportion of those who will deliver within 1 week and help to rationalize their management. The considerable heterogeneity across studies may be indicative of methodological flaws, which either were not reported at all or were under-reported.
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