Department of Mechanical Engineering, Faculty of Engineering of the University of Porto, Porto, Portugal.
Division of Biomechanics, INEGI - Institute of Science and Innovation in Mechanical and Industrial Engineering, Porto, Portugal.
Int J Numer Method Biomed Eng. 2021 Jan;37(1):e3411. doi: 10.1002/cnm.3411. Epub 2020 Nov 8.
During vaginal delivery, the fetal head molds into an elongated shape to adapt to the birth canal, a process known as fetal head molding. However, excessive molding can occur due to prolonged labor or strong contractions, leading to several disorders on the fetal head. This work aims to perform a numerical study on the biomechanics of fetal head molding by measuring specific diameters and the corresponding molding index. A finite element model of the pelvic floor muscles and the fetal body was used. The fetal head is composed of the skin and soft tissues, the skull with sutures and fontanelles, and the brain. The sutures and fontanelles were modeled with membrane elements and characterized by a visco-hyperelastic constitutive model adapted to a plane stress state. Simulations were performed to replicate the second stage of labor in the vertex presentation and occipito-anterior position. With the introduction of viscoelasticity to assess a time-dependent response, a prolonged second stage of labor resulted in higher molding. The pressure exerted by the birth canal and surrounding structures, along with the presence of the pelvic floor muscles, led to a percentage of molding of 9.1%. Regarding the pelvic floor muscles, a 19.4% reduction on the reaction forces and a decrease of 2.58% in muscle stretching was reported, which indicates that sufficient molding may lead to fewer injuries. The present study demonstrates the importance of focusing on the fetus injuries with non-invasive methods that can allow to anticipate complications during labor.
在阴道分娩过程中，胎儿头部会变形为拉长的形状以适应产道，这个过程被称为胎儿头部塑形。然而，由于分娩时间过长或宫缩强烈，可能会出现过度塑形，导致胎儿头部出现多种异常。本研究旨在通过测量特定直径和相应的塑形指数，对胎儿头部塑形的生物力学进行数值研究。我们建立了盆底肌肉和胎儿体的有限元模型。胎儿头部由皮肤和软组织、带有骨缝和囟门的颅骨以及大脑组成。骨缝和囟门采用膜单元建模，并采用适用于平面应力状态的黏弹性超弹性本构模型进行特征化。我们进行了模拟以复制顶先露和枕前位的第二产程。通过引入粘弹性来评估时变响应，第二产程延长会导致更高的塑形。由于产道和周围结构的压力以及盆底肌肉的存在，导致塑形百分比为 9.1%。至于盆底肌肉，报告的反应力减少了 19.4%，肌肉拉伸减少了 2.58%，这表明充分的塑形可能会减少损伤。本研究表明，关注胎儿损伤的重要性，采用非侵入性方法可以在分娩过程中预测并发症。
