Gestational Trimester-Specific Changes in Cervical Length and Their Predictive Value for Preterm Delivery

To investigate gestational age-specific variations in cervical length (CL) and evaluate the predictive ability of CL for preterm delivery (PTD) across different trimesters.

This retrospective longitudinal study included a total of 8659 women who delivered singleton live births between June 1, 2022, and December 31, 2024, at Peking University First Hospital. Associations between CL measured at ≤ 19⁺⁶, 20-24⁺⁶, and 28-33⁺⁶ gestational weeks and PTD were evaluated using receiver operating characteristic curve analysis and log-rank tests.

CL showed substantial variability across gestational ages, with pronounced shortening observed during 28-33⁺⁶ weeks. Significant differences in CL distribution between women with PTD and those with term delivery emerged as early as 20-24⁺⁶ weeks. The predictive value of CL for PTD increased with advancing gestational age. Optimal CL thresholds for predicting PTD ≤ 34⁺⁶ weeks were 28 mm, 15 mm, and 10 mm at ≤ 19⁺⁶, 20-24⁺⁶, and 28-33⁺⁶ weeks, respectively, while corresponding thresholds for PTD < 37 weeks were 28 mm, 26 mm, and 10 mm. Women with CL below these cut-offs had significantly lower probabilities of term delivery. The 26-mm threshold at mid-gestation (20-24⁺⁶ weeks) closely aligned with the conventional 25-mm definition of short cervix, supporting the validity of the minimum P approach. The consistent 10-mm threshold in late gestation suggests that lower diagnostic cut-offs after 28 weeks may be required to guide clinical management.

CL progressively decreases with increasing gestational age and has emerged as a more potent predictor of PTD after 20 weeks of gestation. A short cervix in late pregnancy may be more appropriately defined as < 10 mm at 28-33⁺⁶ gestational weeks.