(1224) Cervical Shortening After Normal Midtrimester Screening: Clinical Implications for Preterm Birth Prediction

Cervical length (CL) screening in the midtrimester is an established method for predicting spontaneous preterm birth (sPTB). However, the clinical implications of cervical shortening diagnosed after a normal midtrimester screening remain unclear. We aimed to examine whether cervical shortening identified at 24.0–34.0 weeks gestation is associated with an increased risk of sPTB, and whether obstetric history modifies this risk.


Study Design:

This retrospective cohort study included 500 singleton pregnancies with normal midtrimester CL who were later diagnosed with cervical shortening (< 25 mm) at 24.0–34.0 weeks gestation at a tertiary medical center between March 2020 and May 2025. Patients were stratified into three groups: CL < 10 mm, 11–15 mm, and 16–25 mm. The primary outcome was sPTB < 37 weeks. Multivariable logistic regression and receiver operating characteristic (ROC) curve analyses were used to evaluate predictive performance. sPTB rates were further analyzed by obstetric history and gestational age at diagnosis.


Results:

sPTB < 37 weeks occurred in 75.0% of patients with CL < 10 mm, 52.5% with CL 11–15 mm, and 25.0% with CL 16–25 mm (p< 0.001). In multivariable models, both CL < 10 mm and 11–15 mm were independently associated with sPTB (adjusted odds ratios [aOR] 8.19 and 3.19, respectively; p< 0.001 for both). Among patients with a CL of 21–25 mm, sPTB rates differed significantly by obstetric history: 26.9% in those with a history of sPTB, 21.8% in nulliparas, and 12.8% in those with a history of term birth (p=0.041) (Figure 1). ROC analysis identified optimal gestational age-specific CL cutoffs of 22 mm (area under the curve [AUC] 0.69) at 24.0–27.6 weeks, 20 mm (AUC 0.62) at 28.0–31.6 weeks, and 18 mm (AUC 0.72) at 32.0–34.0 weeks. A significant increase in the rate of sPTB was observed below these cutoff values (Figure 2).


Conclusion:

Cervical shortening after a normal midtrimester screening was associated with sPTB. Obstetric history modified this risk, particularly in patients with less severe shortening.