Assessment of cervical softening and the prediction of preterm birth (STIPP study); a prospective cohort study

Preterm birth(PTB) is a global health problem and selecting pregnancies at risk is still a challenge. This study evaluates characteristics of cervical softening as a novel biomarker to predict birth in patients presenting with symptoms of threatened PTB. This is a single center cohort study. Pregnancies between 24 ⁺⁰ and 34 ⁺⁰ weeks presenting with symptoms of threatened PTB and intact membranes were included. The cervical stiffness index (CSI) was measured with the Pregnolia® System, providing a quantitative measure of tissue consistency. Lower CSI indicates a softer cervix. Primary outcome was delivery within seven days. We included 163 patients between August 2022 and October 2024 . The primary outcome occurred in 6.5% patients (n=10). Cervical stiffness index was significantly lower in patients delivering within seven days (29.0 mbar [IQR: 24.3-51.8] vs. 69.0 mbar [51.0-90.8]) and adequately discriminated between patients with and without outcome (AUC 0.77 (0.55-0.99)). No correlation between cervical length and CSI was found (ρ=0.12). Patients with a short and soft cervix are most at risk for birth within seven days. A soft cervix, as quantified by a low CSI, in pregnancies with symptoms of threatened PTB is associated with an increased risk of birth within seven days. CSI could be used to distinguish patients with a short cervix who are at risk for preterm birth and could improve risk assessment.