# A biomechanical computational analysis of vacuum-assisted delivery: insights and perspectives

Cédric P. Laurent, Yves Vallet, Charline Bertholdt, Olivier Morel

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Cédric P. Laurent, Yves Vallet, Charline Bertholdt, Olivier Morel. A biomechanical computational analysis of vacuum-assisted delivery: insights and perspectives. Multidisciplinary Biomechanics Journal, 2025, 2, pp.111-113. 10.46298/mbj.16173. hal-05191725v2

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Submitted on 23 Oct 2025

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# A biomechanical computational analysis of vacuum-assisted delivery: insights and perspectives

Cédric Laurent<sup>a, b*</sup>, Yves Vallet<sup>a</sup>, Charline Bertholdt<sup>b, c</sup>, Olivier Morel<sup>b, c</sup>

<sup>a</sup> CNRS UMR 7239 LEM3 - Université de Lorraine, Nancy, France

<sup>b</sup> Université de Lorraine, CHRU-NANCY, Pôle de la Femme, F-54000 Nancy, France

<sup>c</sup> IADI, INSERM U1254, Rue du Morvan, 54500, Vandoeuvre-lès-Nancy, France

* Corresponding author: cedric.laurent@univ-lorraine.fr

Received date: 01/04/2025

Accepted date: 27/06/2025

Publication date: 27/10/2025

**Keywords:** obstetrics, computational modeling, soft tissues biomechanics

© 2025 The Authors

Licence CC-BY 4.0

Published by Société de Biomécanique

## 1. Introduction

Vacuum-assisted delivery (VAD) has become the most common technique among operative vaginal deliveries, as it reduces risks for both fetal and maternal tissues. However, VAD may be associated with rare but potentially serious complications, particularly involving maternal or fetal soft tissue damage. These complications can arise due to variations in vacuum cup placement and clinical technique, both of which are subject to significant heterogeneity. Despite its widespread use, VAD has only recently been examined from an engineering perspective (Goordyal, Anderson, Alazmani, & Culmer, 2021), even though such an approach could improve the understanding of underlying mechanisms in cases of complications. In obstetrics, computational modeling—particularly finite element (FE) modeling—has emerged as a powerful tool, offering a promising alternative to large-scale retrospective studies (Pouca, Ferreira, Parente, Jorge, & Ashton-Miller, 2022). However, FE modeling has not yet been applied to VAD. In this work, we build upon recent studies analyzing the biomechanics of VAD maneuvers performed on training mannequins (Vallet, Lefebvre, et al., 2023) and investigating scalp-to-bone interactions (Vallet, Baldit, et al., 2023). By integrating these insights, we aim to assess the effects of VAD on both maternal and fetal tissues, with a particular focus on the scalp and subcutaneous fascia,

which are implicated in the majority of neonatal complications.

## 2. Methods

### 2.1 Simulation of VAD at the macroscale and associated maternal risk of injuries

A simplified training mannequin (Limbs&Things Ltd, United Kingdom as proposed in (Vallet, Lefebvre, et al., 2023)) was used to validate the approach and investigate the effects of various VAD parameters, including fetal head size, suction cup position, and clinical extraction maneuvers, under controlled geometric and material conditions. A digital twin of the mannequin, based on finite element (FE) modeling, was developed using Abaqus software (Dassault Systèmes) and from the 3D acquisitions of its geometry and mechanical characterization of its constitutive materials considered as 2nd-order Ogden hyperelastic materials for deformable parts and a perfectly rigid bone. Nodes placed on the upper and lower perimeter sections were pinned (see red lines, Fig. 1), constraining only their translation. The reliability of the model was assessed by comparing predicted extraction forces with experimental measurements obtained from vacuum extractions performed using a Kiwi® cup on a mannequin mounted on a force platform (N=16). Additionally, strain fields within the pelvic floor-mimicking tissues were analyzed and correlated with VAD parameters (Fig. 1.a).
<figure><img src="image_2.png" /><figcaption>**Figure 1.** (a) Computational simulation of VAD performed on a training mannequin for validation, and resulting strain fields in maternal soft tissues. (b) Computed strain field within scalp skin during VAD and (c) associated loading of subcutaneous fascias modelled as a series of discrete elements.</figcaption></figure>

Credit: Cédric Laurent.

## 2.2 Simulation of VAD at the mesoscale and associated fetal risk of injuries

The application of a vacuum cup to the fetal head was modeled based on our previous work on the mechanical behavior of skin and subcutaneous fascia. This approach employed a hybrid method, combining standard FE modeling for the skin (Fig.1.b) considered as 2^nd^-order Ogden hyperelastic with a discrete element population to replicate the behavior of the subcutaneous fascia (Fig.1.c) linked to bone consider as a rigid. Elements of the skull base situated at the neck joint were considered attached to a fixed reference point. This modeling framework allowed us to investigate the effects of various VAD parameters on both the scalp and subcutaneous tissues, providing insights into the risk of fetal soft tissue injuries.

## 3. Results and discussion

Representative FE results are presented in Fig. 1, illustrating macroscale deformations in maternal soft tissues and mesoscale mechanical responses in fetal soft tissues. Based on experimental data from vacuum extraction performed on a training mannequin, the FE simulations underestimated the extraction forces (67.5 ± 13.3 N for maximal experimental forces vs. 42.3 N in simulations). However, the simulations accurately reproduced the trends of each force component

throughout the extraction gesture. At the macroscale, the most downward-directed extraction gesture and a more occipital cup placement were found to minimize both extraction force and soft tissue strains. At the mesoscale of fetal tissues, non-significant strains were obtained within the skull sutures and fontanelles, suggesting that VAD forces are primarily transferred to the soft tissues rather than the cranial structures. For the first time, the proposed simulations enabled an investigation of the effects of VAD on fetal soft tissues. A less occipital cup placement was found to minimize strain in the scalp and subcutaneous tissues, aligning with clinical guidelines that recommend positioning the cup at the “pivot point”—a placement that was also found to be optimal in our simulations. Furthermore, the simulated scalp deformation and distribution of subcutaneous tissues closely corresponded to the observed placement and shape of the “chignon” following delivery, as well as to documented patterns of complications and injuries.

## 4. Conclusions

The computational simulations presented in this study serve as powerful tools to: (i) provide insights into the underlying mechanisms of VAD-related complications, (ii) establish guidelines for optimizing VAD use to minimize maternal and fetal soft tissue injuries, (iii) support the design of new vacuum cups or alternative assisted delivery devices, as previously proposed (Vallet, Laurent, Bertholdt, Rahouadj, & Morel, 2022) (iv) develop diverse training scenarios to standardize clinical practices and enhance the safety of VAD in routine obstetric care.

### Conflict of Interest Statement

None.

### Contributor Roles

CL: conceptualization, methodology; funding acquisition, project administration, supervision, validation, writing-original draft; YV: conceptualization, methodology, formal analysis, investigation, software, writing-review & editing; CB: project administration, validation, wrint-review & editing; OM: project administration, validation, wrint-review & editing.

### References

Goordyal, D., Anderson, J., Alazmani, A., & Culmer, P. (2021). An engineering perspective of vacuum assisted delivery devices in obstetrics: A review.
*Proceedings of the Institution of Mechanical Engineers Part H-Journal of Engineering in Medicine*, 235(1), 3–16.
https://doi.org/10.1177/0954411920956467

Pouca, M. C. P. V., Ferreira, J. P. S., Parente, M. P. L., Jorge, R. M. N., & Ashton-Miller, J. A. (2022). On the management of maternal pushing during the second stage of labor: A biomechanical study considering passive tissue fatigue damage accumulation. *American Journal of Obstetrics & Gynecology*, 227(2), 267.e1-267.
e20. https://doi.org/10.1016/j.ajog.2022.01.023

Vallet, Y., Baldit, A., Bertholdt, C., Rahouadj, R., Morel, O., & Laurent, C. (2023). Characterization of the skin-to-bone mechanical interaction on porcine scalp : A combined experimental and computational approach. *Journal of the Mechanical Behavior of Biomedical Materials*, 147, 106139. https://doi.org/10.1016/j.jmbbm.2023.106139

Vallet, Y., Laurent, C., Bertholdt, C., Rahouadj, R., & Morel, O. (2022). Analysis of suction-based gripping strategies in wildlife towards future evolutions of the obstetrical suction cup. *Bioinspiration & Biomimetics*, 17(6). https://doi.org/10.1088/1748-3190/ac9878

Vallet, Y., Lefebvre, J., Laurent, C., Rahouadj, R., Morel, O., & Bertholdt, C. (2023). A preliminary quantification of the clinical gesture during vacuum assisted delivery on a training dummy. *Clinical Biomechanics*, 109, 106093. https://doi.org/10.1016/j.clinbiomech.2023.106093