Ultrasound in Labor & Delivery: From Objective Assessment to Future Innovation

The Evolving Role of Ultrasound in Labor

Intrapartum ultrasound is transforming labor and delivery by providing real-time, objective insights into labor progress, reducing the uncertainty associated with traditional digital vaginal examination (DVE), which is subjective and operator-dependent.^1,2 Transperineal ultrasound offers reproducible, imaging-based assessment that improves clinical confidence and decision-making.^1,2

Modern systems such as GE HealthCare Voluson™ platforms, including applications like Voluson™ SonoL&D, further enhance clinical practice through structured workflows, standardized measurements, and improved documentation. SonoL&D complements manual examination using 2D imaging and semi-automated measurements to evaluate fetal head position and descent during the second stage of labor, while also supporting patient communication through intuitive video and graphic visualization.³

Key benefits include:

• Objective assessment of cervical dilation, fetal head position, station, and descent^1-4
• Higher accuracy and interobserver agreement than DVE^1,2
• Reduced uncertainty and improved clinical confidence^1,2
• Real-time visualization of fetal and maternal anatomy^1-4
• Improved maternal comfort and reduced infection risk^1,2

Ultrasound also enhances workflow and communication:

• Clear documentation and shared understanding among clinicians^2,5
• Support for supervision and decision-making in busy units⁵
• Dynamic monitoring of labor progression using measurable parameters^1-4
• Assessment of caput, skull molding, and fetal head rotation^1-4
• Reliable assessment despite maternal obesity, fetal caput, or examiner variability, where digital examination may be inaccurate or limited^1,6
• Improved efficiency and consistency in care^2,5

Monitoring Labor Progress with Ultrasound

Transperineal ultrasound enables dynamic, repeatable assessment of fetal descent and cervical changes, providing objective insight into labor biomechanics.^1,2,8 Clinicians can efficiently obtain key measurements—such as the angle of progression (AoP), head–perineum distance (HPD), and midline angle (MA)—to support decision-making during active labor.

Common parameters include:
• Fetal descent (AoP, HPD)^1-4,6-8
• Sonographic cervical dilation (SCD)^1-3
• Caput formation and skull adaptation^1,2,5
• Fetal head position, rotation, and alignment^1-3

Angle of Progression (AoP)

The AoP is a well-established parameter for assessing fetal head descent and predicting delivery outcomes.⁷ It is measured in the sagittal plane between the axis of the pubic symphysis and a line tangential to the fetal skull.^4,7 Larger angles indicate greater descent and are associated with successful vaginal or operative delivery.⁷ Serial measurements allow reliable tracking of labor progression and are more accurate than digital examination when interpreted alongside other parameters.^1-4

SonoL&D assisted documentation of Angle of Progression

Head–Perineum Distance (HPD) and Cervical Assessment

HPD measures the shortest distance between the fetal skull and perineum and decreases as labor progresses.^1,2,8 Repeated measurements provide an objective method to assess descent, especially when caput limits clinical examination.^2,8

Ultrasound also enables estimation of cervical dilation (SCD), offering a less invasive and more objective alternative to manual assessment.^1,2

Fetal Skull Adaptation and Rotation

Transperineal ultrasound allows visualization of caput succedaneum and fetal skull molding, improving understanding of labor mechanics. It also enables assessment of fetal head rotation via parameters such as the midline angle, which is essential for safe operative delivery. ^2,5

Additional signs, such as the “head up sign” and perineal muscle activity, can further inform labor progress and clinical decisions.^2,5

Practical Considerations

For optimal imaging, the maternal bladder should be empty.¹ Visualization may be limited when the fetal head is high, and gentle probe pressure is required to ensure image quality while maintaining patient comfort.¹ Intrapartum ultrasound is particularly valuable in prolonged labor or when repeated assessment is needed.²

Clinical Value and Future Directions

Ultrasound enhances safety in operative vaginal delivery by confirming fetal head position and guiding correct forceps placement in real time.^1,2,9 It also improves patient communication, as visual imaging and graphics help patients better understand labor progress and participate in decision-making.¹

Current guidelines, including those from the Royal College of Obstetricians and Gynaecologists, recommend ultrasound assessment when fetal head position is uncertain, reinforcing its clinical value.^1,9

Future developments include:

• AI-assisted measurements to improve reproducibility²
• Sonopartograms for visualizing labor progression²
• Predictive models combining ultrasound and clinical data²
• Expanded applications in pelvimetry and biomechanics²

Ultimately, intrapartum ultrasound improves accuracy, safety, and communication in labor management, particularly during the second stage, enabling more informed clinical decision-making.^1,2 It enables continuous, data-driven monitoring of labor and supports more personalized care.^1,2

References

1. Ghi T, Eggebø TM, Lees C, et al. ISUOG Practice Guidelines: intrapartum ultrasound. Ultrasound in Obstetrics & Gynecology. 2018.
2. Ramirez Zegarra R, Lizarraga Cepeda E, Ghi T. Intrapartum ultrasound. Best Pract Res Clin Obstet Gynaecol. 2025;101:102617.
3. https://womens-health.net/clinical-specialty/labor-delivery/sonold-benefits
4. Taychaburapanone P, Pongchaikaikiti P, Onraksa W, Chindasombatcharoen S, Suntipap M. Transperineal ultrasonography angle of progression measurement as a predictor of successful labor in pregnancy with induction of labor: a systematic review and meta-analysis. J Matern Fetal Neonatal Med. 2025;38(1):2537231.
5. Malvasi A, Tinelli A. Intrapartum Ultrasonography for Labor Management. Springer. 2016.
6. Malvasi A, Baldini GM, Difonzo T, Cerbone M, Cara I, Demarco M, Mappa I, Rizzo G, Vimercati A, Dellino M, et al. Intrapartum Ultrasound in Vacuum Operative Delivery: A Comprehensive Review and Proposal of the Novel Ultrasound Flexion Point Method. Diagnostics. 2026; 16(6):946.
7. Barbera AF, Pombar X, Perugino G, Lezotte DC, Hobbins JC. A new method to assess fetal head descent in labor with transperineal ultrasound: the angle of progression. American Journal of Obstetrics and Gynecology. 2009.
8. Eggebø TM, Gjessing LK, Heien C, et al. Prediction of labor and delivery by transperineal ultrasound in the second stage of labor. Ultrasound in Obstetrics & Gynecology. 2008.
9. Royal College of Obstetricians and Gynaecologists. Operative Vaginal Delivery. Green-top Guideline No. 26. Updated 2020. RCOG; 2020.

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