Induction of labor accounts for 20-30% of deliveries in high-income countries. The decision to induce, or how to prepare the cervix beforehand, still relies largely on a manual examination developed sixty years ago. As induction volumes rise and patient populations diversify, more clinicians are asking whether that exam still deserves its central role and what an objective alternative could look like in daily practice.
Bishop Score Assessment: How the Standard Clinical Scoring System Works
In 1964, Edward Bishop introduced his pelvic scoring system to help in the selection of appropriate patients for elective induction of labor and predict its success. The best candidates would be the ones who were likely to spontaneously labor in the near future, presenting a “favorable” cervix.
The score evaluates five clinical parameters of the cervix (dilation, effacement, position, consistency, and fetal station) into a total ranging from 0 to 13. A modified Bishop score includes cervical length instead of effacement, with a maximum score of 12. There is no precise, established criterion defining a cervix as favorable or unfavorable for induction, but a score above 8 using the traditional Bishop scoring system, or a threshold of 5 or higher in the modified version, is generally considered favorable.
Anatomically, the score reflects the cervical remodeling necessary for the fetus to be delivered. As pregnancy progresses, collagen density decreases while hyaluronic acid and water content rise. When delivery approaches, rising prostaglandin activity drives further collagen breakdown, softening, and dilation. The Bishop score attempts to capture this process through touch and visual inspection. It requires no equipment and remains, by most guidelines, the standard starting point for deciding whether cervical ripening is needed before oxytocin, prostaglandins, or mechanical methods are used.
Why Clinicians Are Seeking a Bishop Score Alternative
Bishop’s original cohort consisted exclusively of multiparous women with a prior vaginal delivery, induced with methods such as oxytocin, membrane stripping, and amniotomy, very different from today’s balloon catheters and staged prostaglandin protocols. Today, the score is routinely applied also to nulliparous women, irrespective of past pregnancy history, whom Bishop explicitly excluded from his study.
With the current approaches, low Bishop scores are not always predictive of a cesarean delivery, as demonstrated by the ARRIVE trial. The trial found no significant reduction in cesarean risk by Bishop score subgroup when nulliparous women were induced at 39 weeks, an unexpected result, given decades of assumed correlation between an unfavorable score and cesarean risk (Grobman et al., 2018).
As maternal-fetal medicine specialist Helen Feltovich argues in Interface Focus, labor is at its core a biomechanical event, and neither cervical length nor a subjectively scored digital exam captures the tissue mechanics that actually govern how and when a cervix opens. The cervical softness and microstructural organization can be objectively quantified, and these properties change dramatically as pregnancy advances, which is impossible to register by manual examination. On top of that, it is hard to ignore the well-documented interobserver variability inherent to Bishop’s score. There is a growing need for an operator-independent alternative that takes into account cervical biomechanics.
Biomechanical Cervical Assessment as an Objective Alternative
Elastography is a non-invasive, more objective alternative for assessing cervical stiffness changes during pregnancy. A 2016 systematic review and meta-analysis in the Journal of Perinatal Medicine, pooling four studies and 323 women, found that cervical elastography shows a superior accuracy compared to the Bishop score. It could be used not only for a more reliable cervical stiffness assessment, but also for a better prediction of labor induction success (Londero et al., 2016).
Elastography can be generated through manual compression (strain elastography) or through an internally generated shear wave (shear wave elastography, SWE), with the latter offering an absolute, operator-independent stiffness value. For the cervix specifically, 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.
Torsional wave elastography (TWE) is an emerging alternative that addresses both this and the reflection artifacts that smaller organs are prone to. TWE is based on shear elastic waves that propagate through soft biological tissues in a curled geometry, both radially and in depth. Unlike conventional ultrasound waves, their strong sensitivity to changes in tissue consistency makes them especially suited for characterizing the mechanical properties of organs such as the cervix.
Clinical Evidence and Integration into Existing Workflows
CerviSense turns TWE into a bedside tool. A handheld CE-marked intravaginal probe propagates the torsional wave and captures its distortion through an integrated sensor system, converting it into a cervical stiffness reading in kilopascals within seconds. The platform combines this measurement with condition-specific clinical variables through AI-driven risk models spanning the full pregnancy timeline: preterm labor risk prediction at the second trimester scan (week 16-23 of Gestational Age), threatened preterm labor assessment from week 24 of Gestational Age onward, and post-terminduction-of-labor readiness from week 37 onward.
We have demonstrated that TWE is a tool that allows quantifying cervical shear stiffness during pregnancy and that the technique is safe to be used in pregnant women (Massó et al., 2019). We have also validated the underlying TWE physics. A 2024 study in Scientific Reports tested the torsional wave probe on calibrated tissue phantoms and found its stiffness measurements correlated with shear wave elastography at greater than 95%, with consistent, repeatable readings across trials (García et al., 2024). That same measurement principle has already cleared the reproducibility bar in real patients: we have validated the torsional wave probe in a multicenter study for threatened preterm labor assessment, reporting an intraobserver ICC of 0.88 and, after refinement, an interobserver ICC of 0.93 (Molina et al., 2023).
We are now working to extend this validated measurement principle to the induction of labor through CerviSense’s AI Model III, aiming to predict delivery success and help reduce emergency cesarean sections at week 37 and beyond. We are in the preparation phase of a clinical trial carried out in Sweden, Marburg (Germany) and Torrejón de Ardoz (Spain) with an aggregated sample size of 500 patients.
We aim to transform diagnostics for better women’s health by combining the novel torsional wave technology with AI.
Sources
Callejas A, Melchor J, Faris IH, Rus G. Viscoelastic model characterization of human cervical tissue by torsional waves. J Mech Behav Biomed Mater. 2021 Mar;115:104261. doi: 10.1016/j.jmbbm.2020.104261.
Feltovich H. Labour and delivery: a clinician’s perspective on a biomechanics problem. Interface Focus. 2019 Oct 6;9(5):20190032. doi: 10.1098/rsfs.2019.0032.
García A et al. Reliability and robustness of a novel preclinical torsional wave-based device for stiffness evaluation. Sci Rep. 2024; 14, 16461. doi:10.1038/s41598-024-66661-2
Grobman WA et al. Labor Induction versus Expectant Management in Low-Risk Nulliparous Women. N Engl J Med. 2018 Aug 9;379(6):513-523. doi: 10.1056/NEJMoa1800566.
Kim H, Hwang HS. Elastographic measurement of the cervix during pregnancy: Current status and future challenges. Obstet Gynecol Sci. 2017 Jan;60(1):1-7. doi: 10.5468/ogs.2017.60.1.1.
Kuba K, Kirby MA, Hughes F, Yellon SM. Reassessing the Bishop score in clinical practice for induction of labor leading to vaginal delivery and for evaluation of cervix ripening. Placenta Reprod Med. 2023 Jan 31;2:8. doi: 10.54844/prm.2023.
Londero AP et al. Diagnostic accuracy of cervical elastography in predicting labor induction success: a systematic review and meta-analysis. J Perinat Med. 2016 Mar;44(2):167-78. doi: 10.1515/jpm-2015-0035.
Massó P, Callejas A, Melchor J, Molina FS, Rus G. In Vivo Measurement of Cervical Elasticity on Pregnant Women by Torsional Wave Technique: A Preliminary Study. Sensors (Basel). 2019 Jul 24;19(15):3249. doi: 10.3390/s19153249.
Molina FS et al. Reproducibility and usability assessment of the novel Fine Birth device for threatened preterm labor diagnosis. Am J Obstet Gynecol MFM. 2023 Jul;5(7):100982. doi: 10.1016/j.ajogmf.2023.100982.
Swiatkowska-Freund M, Preis K. Cervical elastography during pregnancy: clinical perspectives. Int J Womens Health. 2017 Apr 21;9:245-254. doi: 10.2147/IJWH.S106321.
Wormer KC, Bauer A, Williford AE. Bishop Score. [Updated 2024 Jul 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470368/
