Cervical assessment in obstetrics still relies on tools that only capture part of the picture: a manual exam, a length measurement, a biomarker test. None of them tells a clinician how the tissue itself is behaving mechanically, information that matters for predicting preterm birth and induction outcomes alike. Shear wave elastography (SWE) has emerged as an answer to that gap, and this article walks through the physics behind it, where the clinical evidence stands, and what to look for when evaluating an SWE-capable device for your department.
What Is Shear Wave Elastography? Principles and How It Differs from Strain Elastography
Elastography quantifies how a tissue responds to a mechanical stimulus: softer tissue deforms more easily than firm tissue, and this contrast translates into a stiffness value. The technique branches into two families depending on how that impulse is generated.
Strain elastography measures tissue displacement under manual probe compression and renders the result as a color-coded map. It is intuitive and low-cost, but cannot report an absolute stiffness value, only a relative one, since the cervix has no adjacent reference tissue to compare against.
Conventional shear wave elastography uses an ultrasonic push to generate the impulse and measures the speed of the resulting shear wave as it travels through tissue. A focused ultrasound beam displaces the tissue at a single point, generating a shear wave that propagates perpendicular to the beam’s direction. Because this wave travels through stiff tissue far faster than through soft tissue, the system builds a real-time color map of that speed across the image — soft areas in blue, stiff areas in red. Placing a region of interest on that map returns a quantitative stiffness value, expressed as shear wave velocity (m/s) or Young’s modulus (kPa) depending on the system.
Clinical Applications of SWE in Obstetric Practice
Cervical stiffness assessment for preterm birth risk stratification
Although the Bishop score has been a widely used digital examination of the cervix for decades, it is now used less often because it is too invasive and subjective. Transvaginal ultrasound measurement of cervical length (CL) and detection of fetal fibronectin in cervicovaginal secretions remain the standard approaches for assessing preterm birth risk. These techniques account for false-positive rates of 70 and 75%, respectively, leading to unnecessary hospitalizations, tocolytics administration, healthcare costs, and waste of resources.
Up to 60% of spontaneous preterm births occur in women with normal CL. A cervix can stay anatomically long while the internal os, the region responsible for maintaining pregnancy, is already softening beneath the surface. Because the internal os cannot be assessed manually, elastography is the only tool that reaches it and gives information about the biomechanical state of the cervix.
Studies assessing internal os stiffness using strain elastography in low-risk populations at 18–22 weeks found that a soft internal os was associated with substantially higher rates of subsequent preterm delivery than a firm one, with figures as high as 81.1% versus 1.7% in one prospective cohort (Wozniak et al., 2014). Shear wave measurements in the prediction of preterm labor were reported for the first time in 2015. Shear wave speed specifically correlates with gestational age, with the presence of preterm contractions, and with the risk of preterm delivery (Muller et al., 2015), reinforcing the case for combining stiffness data with cervical length rather than relying on length alone.
A 2025 systematic review and meta-analysis pooling 13 studies and 4,087 women confirms this predictive value for preterm birth: cervical elastography correctly flagged roughly three out of every four women who ultimately delivered preterm (Angelopoulou et al., 2025). SWE showed higher sensitivity later in gestation, and strain elastography performed comparatively better earlier on.
Induction readiness: complementing and replacing the Bishop Score
The Bishop score was developed on a cohort of multiparous women with prior vaginal deliveries, using induction methods that bear little resemblance to today’s balloon catheters and staged prostaglandin protocols. It is now applied indiscriminately to nulliparous women, whom Bishop explicitly excluded. The ARRIVE trial found no significant reduction in cesarean risk by Bishop score subgroup among nulliparous women induced at 39 weeks, an unexpected result given decades of assumed correlation (Grobman et al., 2018).
Elastography has consistently outperformed the Bishop score on this question. A 2016 meta-analysis pooling four studies and 323 women found cervical elastography superior to the Bishop score for predicting labor induction success (Londero et al., 2016). In a prospective study of 475 women undergoing induction, cervical SWE measured across the inner, middle, and outer regions of the cervix is a useful predictor of cesarean section. The combination of sonographic cervical length and elastography is superior to the Bishop score in the prediction of the outcome of labor induction (Lu et al., 2020).
How to Select a Shear Wave Elastography-Capable Device for Your Department
Conventional shear wave elastography has real limitations. Because shear waves lose strength quickly as they travel, the technique works best on tissue close to the probe and becomes less reliable at depth. It’s also sensitive to how the tissue is being handled: pressing the probe too firmly can artificially stiffen the reading before the measurement even starts. And because different systems use different scanning parameters, results aren’t always directly comparable from one machine to another.
Although it is more objective than strain elastography, conventional SWE presumes that the tissue is homogeneous, non-viscous, and isotropic, conditions the cervix does not meet, given its heterogeneous, anisotropic, and highly hydrated structure. Commercial shear wave transducers also struggle to isolate a pure shear signal from longitudinal waves, which can produce multiple reflections in a small organ like the cervix.
Torsional wave elastography (TWE) is an emerging alternative that addresses both issues directly. These shear waves travel through soft tissue in a curled pattern instead of a straight line, which helps them avoid the reflection problems that affect conventional shear waves in a small organ like the cervix.
CerviSense turns this physics into a practical bedside tool. It is a handheld, CE-marked, intravaginal probe that generates a torsional wave and converts its propagation into a cervical stiffness reading, in kilopascals, within seconds. Its lateral microcamera lets the clinician visualize the anterior cervix while taking the measurement. The resulting stiffness value feeds directly into AI-driven risk models covering threatened preterm labor, preterm labor, and induction-of-labor readiness, giving a single device continuous coverage across the pregnancy timeline. It combines what clinicians need: an intuitive, easy-to-use device that operates as a standalone unit and fits into a routine antenatal visit without extensive retraining.
Evidence Base and Integration Pathway for Clinical Adoption of Torsional Waves
CerviSense has demonstrated a 41% increase in reproducibility among users compared with transvaginal ultrasound. CerviSense’s interobserver ICC of 0.93, achieved after adding a lateral microcamera to guide probe placement, also sits at or above the upper end of the ranges published for cervical shear elastography, while removing the region-dependent variability. A study of SWE in 120 pregnant women reported interobserver ICC values ranging from 0.34 to 0.86 depending on the cervical region measured (Suthasmalee and Moungmaithong, 2019), and a separate analysis of SWE reproducibility across 200 non-pregnant patients found interrater ICCs between 0.83 and 0.92 (O’Hara, Zelesco and Sun, 2019).
This result adds to a broader body of evidence: CerviSense is safe for use in pregnant women (Massó et al., 2019), and its underlying physics have been validated against established shear wave techniques (García et al., 2024). The pathway is now moving into larger prospective trials across indications. The FB-CT2 pivotal study is currently enrolling 457 patients across Spain and Germany for threatened preterm labor, and QEPS is following 1,000 patients in the UK for spontaneous preterm labor. For induction of labor, CerviSense is entering a 500-patient trial in Sweden (MATERN-AID), to give departments one consistent, validated tool across the full pregnancy timeline rather than a different device for each clinical decision point.
As this evidence base matures, torsional wave elastography is positioned to move from a promising alternative to a standard of care for objective cervical assessment throughout pregnancy.
Sources
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