Predictive value of cervical length measured after 24 weeks for spontaneous preterm birth: systematic review and...

This study aimed to investigate the differences in transvaginal cervical length after 24⁺⁰ weeks of gestation between women with spontaneous preterm birth and term birth and the predictive accuracy of third trimester transvaginal cervical length in the prediction of spontaneous preterm birth among asymptomatic women.

A systematic search of published literature was performed in PubMed, MEDLINE, and the Cochrane Library through June 2025. There was no language restriction.

Cohort or cross-sectional studies reporting on transvaginal cervical length measurements after 24⁺⁰ weeks of gestation in asymptomatic women with both spontaneous preterm birth and term births that allowed the construction of 2×2 contingency tables were included. We excluded abstracts, studies with duplicated data, symptomatic women, twin pregnancies, or transabdominal cervical length measurement (International Prospective Register of Systematic Reviews registration number: CRD42024538449).

T.S.T.A. and T.Y.P.C. searched for and selected studies independently. Newcastle-Ottawa Scale was used to evaluate the quality of the included studies. Mean differences in transvaginal cervical length measurements between spontaneous preterm birth and term populations were calculated using the inverse variance method with the random-effects model. Subgroup analyses on gestational age, transvaginal cervical length measurement technique, populations, and type of cohort studies were performed. Predictive accuracy of various transvaginal cervical length cutoffs was evaluated using the DerSimonian-Laird random-effects model. Youden index was calculated to identify the optimal transvaginal cervical length cutoff.

A total of 3641 published articles were identified and 16 studies consisting of 26,776 pregnancies met the inclusion criteria. All studies excluded iatrogenic preterm birth. Women with spontaneous preterm birth had a significantly shorter transvaginal cervical length at 24⁺⁰ to 28⁺⁶ weeks (<37 weeks: mean difference=-5.47, 95% confidence interval=-7.52 to -3.43, P<.001; <34 weeks: mean difference=-7.85, 95% confidence interval=-10.33 to -5.37, P<.001) and 27⁺⁰ to 32⁺⁶ weeks (<37 weeks: mean difference=-4.41, 95% confidence interval=-6.45 to -2.36, P<.001; <34 weeks: mean difference=-7.75, 95% confidence interval=-10.55 to -4.94, P<.001), compared to women with term birth. The transvaginal cervical length at 31⁺⁰ to 36⁺⁶ was comparable between the 2 groups (<37 weeks: mean difference=-4.71, 95% confidence interval=-10.13 to 0.72, P=.09). These observations were consistently seen among women with or without risk factors for spontaneous preterm birth, and irrespective of the transvaginal cervical length measurement method. A transvaginal cervical length cutoff of 25.5 to 26.0 mm after 24⁺⁰ weeks had the highest positive likelihood ratio of 7.75 to predict spontaneous preterm birth, with pooled sensitivity of 0.74, specificity of 0.92, negative likelihood ratio of 0.31, and diagnostic odds ratio of 28.1.

Women with spontaneous preterm birth had a significantly shorter transvaginal cervical length after 24⁺⁰ weeks of gestation, compared to those who delivered at term. A cutoff of 25.5 mm between 24⁺⁰ and 32⁺⁶ weeks may be used to identify women at risk of spontaneous preterm birth.