Perineal deformation during forceps, vacuum and OdonAssist™ assisted vaginal deliveries: A simulation study based on advanced image processing

Objectives: The aim of this study was to analyse influence of the fetal head position and the type of instrument used (forceps, vacuum, OdonAssist™) on perineal deformation, during simulated vaginal deliveries monitored by stereophotogrammetry.

Methods: An exploratory study was conducted using mannequins simulating vaginal births. Fifty simulated deliveries were performed with different fetal head positions and instruments: Pajot's forceps, Kiwi-vacuum, and OdonAssist™. Stereophotogrammetry measured perineal deformations called equivalent strains E_eq.

Results: E_eq during spontaneous deliveries were minimal, average, and maximal at 0.8 %, 5.8 %, and 11.6 %, respectively. Assisted vaginal births (AVB) showed slightly higher strains compared to spontaneous deliveries. In the occipito-posterior position (OP), strains were significantly higher (p < 0.05). Equivalent strain Eeq trend towards higher mean (6.7 ± 0.6 %) and maximum (12.3 ± 0.8 %) with forceps compared to other methods in the occiput anterior position (OA), especially against spontaneous (mean: 5.3 ± 0.5 % and max: 9.9 ± 0.6; p = 0.06), vacuum AVB (mean: 4.6 ± 1.0 % and max: 9.4 ± 0.1 %, p = 0.06) and OdonAssist™ AVB (mean: 3.8 ± 0.9 % and max: 8.8 ± 1.0 %, p = 0.06). Forceps induced greater strains compared to vacuum and OdonAssits™. In OP position, OdonAssist™ tend to lower mean equivalent strain E_eq compared to spontaneous vaginal deliveries (4.9 ± 0.6 % vs 6.4 ± 0.5 %, p = 0.06).

Conclusion: Results confirmed increased mechanical perineal stress for OP fetal position and for forceps assisted deliveries compared to others devices. The OdonAssist™ may offer a less invasive alternative, reducing perineal strains. Stereophotogrammetry provides valuable data on the mechanical effects of childbirth.