1. Introduction
Most of obstetricians observe a great variability between women for the mode of delivery (cesarean section, operative delivery) and perineal tears that could occurred at childbirth (superficial tear to severe tears involving the anal sphincter complex). One hypothesis for these individual susceptibilities is that the intrinsic biomechanical characteristics of women could be associated with these outcomes. These characteristics could have a major impact for the management of the delivery in term of postural management in order to optimize the mechanism of childbirth but also in risk prediction and prevention of perineal trauma at childbirth. The objective of this paper is to provide synthetic analysis of the literature available to justify the introduction of biomechanical considerations into the obstetrical management of childbirth.
2. Methods
The authors performed a literature analysis about the association between biomechanical considerations and both the optimization of the mode of delivery and the perineal trauma risk prediction/prevention. Papers have been selected based on a PubMed research using the following keywords: childbirth, position, biomechanics, pelvic floor, obstetric anal sphincter injury, pregnancy, pelvic floor muscles, elastography.
Highlighted with this literature review, we’ll report the interest of considering pregnant women’s intrinsic biomechanical characteristics for the management of childbirth. The discussion will be supported by recent original works on this thematic. Finally, we’ll discuss the prospects that might be offered by the implementation of biomechanical affects in obstetrical management.
3. Results and discussion
3.1. Optimization of childbirth using postural management
The increase rates of cesarean section have led major obstetrical organizations worldwide to issue recommendations. These initiatives have allowed a stabilization but not a decrease in cesarean section rates, suggesting that novel complementary approaches are required. Current recommendations rely mainly on clinical or epidemiological obstetrical research, with little consideration for the biomechanical aspects of labor. Approximatively 30% of emergency cesarean sections are due to dystocia, which is defined as a slow and abnormal progression of labor. Dystocia is mainly a biomechanical complication and emerging hypotheses posit that mobilizing the lumbar-pelvic-thigh complex of women in labor (parturients) could allow better progression of the fetus, and thus reduce the number of emergency cesarean sections. The orientation of the pelvis (pelvic inlet plane) relative to the fetal axis trajectory, the flatness of the lumbar spine and uterine contractions are three of the most critical factors in labor. They are particularly important actors with regard to dystocia because they control the movement of the fetus towards the birth canal. Surprisingly, little has been done to monitor these aspects and understand their exact roles. Recently, it was shown that mobilizing the women’s lumbar-pelvic-thigh complex influences the relative orientation of the pelvis and the lumbar spine flatness, suggesting that dystocia could be addressed by optimal mobilization of the parturients. While promising, further research and technical development are necessary before the concept of optimal lumbarpelvic-thigh complex mobilization could be used in the clinics.
3.2. Perineal trauma prediction and prevention
It has been reported that during pregnancy, there is an increase in ligamentous laxity and that it is associated with perineal trauma occurrence. Indeed, women with the greatest ligamentous laxity had the most important risk of perineal trauma. This suggest that women with the weakest tissues may have the greatest risk of pelvic floor trauma. This is supported by the observation of that tissues with a weak stiffness raise easily their plasticity threshold. One limit of such a work is that it is based on biomechanical measures on the upper limb, which is quite different of pelvic floor muscles considerations. There are some animal data published which report biomechanical changes in pelvic floor properties during pregnancy: increase in muscle fiber length (increase of number of sarcomeres in series) and increase in pelvic floor muscle stiffness. This phenomenon might be a protective process from pelvic floor trauma at childbirth. Nevertheless, to date there are no human data supporting these results. Recent works report some possibilities to assess in vivo and directly the elastic properties of women’s pelvic floor (vaginal elastometer, ultrasound). One of the most interesting technique is the shear wave elastography technology which allow a quantitative direct assessment of muscles stiffness. A feasibility study reports the possibility to assess the levator ani muscle with this technique in non-pregnant women. This technique is quite promising since every pregnant woman undergo at least three ultrasound examinations during its pregnancy. If, during one of these examinations we could perform a pelvic floor muscle assessment that indicate if the woman is at low or high risk of perineal trauma, it will allow individualized information and implementation of preventive strategies. A prospective study is ongoing about the characterization of pelvic floor muscle elastic properties during pregnancy and its impact on perineal trauma risk. These data will probably lead to a better identification of high-risk women allowing an individualized information and preventive strategies implementation.
4. Conclusions
It appears that the intrinsic biomechanical characteristics of pregnant women are probably involved with both their mode of delivery and their risk of perineal trauma at childbirth.
Including biomechanical considerations in our management of childbirth will probably lead to offer an individualized care to pregnant women. It will allow an individualized risk assessment about their risk of pelvic floor trauma and an individualized optimization of the mechanisms of their delivery.
References
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