Alteration and Predictive Ability of Cervical Length for Preterm Delivery in Each Gestational Trimester

Abstract Background To investigate the variations in cervical length (CL) across the first, second and third trimesters and the association with preterm delivery (PTD). Methods In total, 16,352 women (32,543 measurements) who delivered singleton live births between January 1, 2020, and October 31, 2023, at Peking University First Hospitals were included in the present study. The associations between CL at three gestational weeks (9–13⁺ ⁶, 19–23⁺ ⁶ and 29–33⁺ ⁶ weeks) and PTD were evaluated using receiver operating characteristic (ROC) curves and logistic regression analysis. The chi-square test was used for comparisons of the incidence of PTD at or below each percentile for CL with patients with CL above the 75th percentile. Results With increasing gestational age, there was a downward trend in CL at each percentile, with particularly obvious decreases in the 10th (31.5 mm and 27.1 mm), 5th (30.0 mm and 23.4 mm) and 1st (25.2 mm and 15.5 mm) percentiles after the 19th week of gestation. As gestational age increased, the predictive value of CL for PTD ≤ 34⁺ ⁶ gestational weeks and PTD < 37 gestational weeks increased. After the 19th week of gestation, CL and PTD risk were negatively correlated when CL was less than or equal to the 75th percentile (all P < 0.01). The incidence of PTD < 37 gestational weeks was significantly higher among women with CL ≤ 22.3 mm at 29–33⁺ ⁶ gestational weeks than among women with CL ≤ 25 mm. Conclusions CL progressively decreases with increasing gestational age and has emerged as a more potent predictor of PTD after the 19th week of gestation. The defining threshold of a short cervix should probably be less than 25 mm at 29–33⁺ ⁶ gestational weeks.