Objective:

To evaluate whether longitudinal changes in cervical length (CL) between the 1st and 2nd trimesters add predictive value for spontaneous preterm birth (sPTB) in women with a normal mid-trimester cervix.

Approach:

• Study Design: A prospective longitudinal cohort study including singleton pregnancies with 1st and 2nd trimester transvaginal CL measurements.
• Cohorts: Women with a normal mid-trimester cervix formed the primary low-risk cohort; women with a short cervix were analyzed separately.
• Measurements: Cervical length was measured at 11–14 weeks (C1) and 18–24 weeks (C2), with ΔCx and cervical slope calculated.
• Outcomes: The primary outcome was sPTB <37 weeks, with additional analyses on preterm prelabor rupture of membranes (PPROM) and PROM at term.

Key Findings:

• The overall rate of sPTB was 8.00% in the low-risk cohort and 30.6% in the short cervix cohort (p<0.001).
• Cervical length measurements (C1, C2, ΔCx) and cervical slope were similar between term and preterm pregnancies in the low-risk cohort (p > 0.05).
• Cervical slope was not associated with sPTB and did not improve discrimination beyond C2 and maternal characteristics.
• The short-cervix cohort had significantly shorter C1 and C2 measurements and a more negative cervical slope (p < 0.001).
• PPROM was more frequent among preterm births in the low-risk cohort, and cervical slope was associated with PPROM (p = 0.030).

Interpretation:

Longitudinal changes in cervical length do not enhance the prediction of sPTB beyond a single 2nd trimester measurement in women with a normal mid-trimester cervix.

Limitations:

• The study excluded women with a short cervix from the primary analysis, limiting the generalizability of findings.
• The sample size for the exploratory short-cervix cohort was relatively small.

Conclusion:

The clinical value of cervical screening primarily lies in identifying the short-cervix subgroup.