Cervical Stiffness Assessment in High-risk Pregnancies for Preterm Birth

This is a prospective, non-interventional, post-market monocentric clinical investigation in a Swiss hospital (Lucerne Cantonal Hospital) to measure cervical stiffness on women at high risk of premature birth, defined as women with a cervical length less or equal to 25 mm presenting between 16+0 wp and 32 wp. Cervical stiffness will be measured as Cervical Stiffness Index (CSI) using the Pregnolia System. The primary objective is an initial characterization of the distribution of the median Cervical Stiffness Index (CSI, in mbar), corresponding to the median of three consecutive measurements at each presentation at pregnant women of gestational age between 16weeks 0 days and 32weeks 0 days with a cervical length less or equal to 25 mm before the initiation of progesterone treatment. Day 1 is when study inclusion criteria are met, informed consent is obtained and the first Cervical Stiffness Index is carried out. Secondary objectives * At each presentation three consecutive CSI measurements will be carried out and as a secondary objective the first, the highest, lowest and mean measurement will be analyzed for each secondary outcome. * Evaluation of Cervical Stiffness Index 1, 2, 3 (CSI, in mbar) on day 10-14 and on day 24-28 after initiation of progesterone treatment, which is defined as day 1; further follow-up is not mandatory, but possible * Determination of a first estimate of the correlation of the initial CSI and CSI changes with birth outcome (gestational age at birth) * Determination of a first estimate of the correlation of CSI with cervical length (longer cervical length stiffer?) * Determination of first signals for potential associations of CSI with additional treatments for preterm birth (tocolysis, cerclage, pessary) * Determination of first signals for potential associations of CSI with neonatal outcome (birth weight, APGAR, arterial pH, admission to neonatal intensive care) * Safety objective: safety of the device, by assessing incidence, severity, and seriousness of device-related adverse events (discomfort, bleeding, lesion, irritation).