Cervical Stiffness Index as predictor of preterm birth in women with threatened preterm labor

To determine the uterine cervix stiffness in patients presenting with threatened preterm labor (PTL) measured with an aspiration-based device (expressed as Cervical Stiffness Index - CSI) and to correlate CSI with pregnancy outcomes.

Single-center, prospective, observational pilot study of patients with singleton pregnancies presenting with threatened PTL between 24^0/7 and 33^6/7 weeks. Patients underwent a physical examination, ultrasound examination, transvaginal ultrasound cervical length (CL) measurement and cervical stiffness assessment using the Pregnolia System, an aspiration-based device measuring the vacuum required to displace the tissue into the device tip by a fixed distance, a proxy for stiffness (CSI, mbar). Higher CSI indicates stiffer tissue.

Between April 2022 and August 2024, 100 patients with signs and symptoms of PTL were recruited. Thirty-five had a PTB, of which 7 delivered < 34 weeks, 5 within 14 days and 11 within 28 days from measurement. CSI and CL were significantly different between patients delivering at term and patients with a PTB. The Area under the Curve of CSI and CL for prediction of delivery ≤ 14 days from measurement were 0.979 (95 % CI, 0.952-1.000) and 0.744 (0.369-1.000), respectively; for delivery ≤ 28 days from measurement, 0.802 (0.612-0.993), and 0.764 (0.579-0.948), respectively; for PTB < 34 weeks, 0.873 (0.729-1.000) and 0.836 (0.563-1.000), respectively; and for PTB < 37 weeks 0.845 (0.763-0.926) and 0.779 (0.680-0.877), respectively.

In patients presenting with threatened PTL, a softer cervix as measured by CSI was associated with an increased risk of preterm birth. These findings suggest that CSI has potential as a predictor of PTB in symptomatic patients, but require confirmation in larger, independent cohorts.

NCT05355649.