Date Published: May 15, 2019
Publisher: Public Library of Science
Author(s): Olivier Ami, Jean Christophe Maran, Petra Gabor, Eric B. Whitacre, Dominique Musset, Claude Dubray, Gérard Mage, Louis Boyer, Nick Todd.
To demonstrate and describe fetal head molding and brain shape changes during delivery, we used three-dimensional (3D) magnetic resonance imaging (MRI) and 3D finite element mesh reconstructions to compare the fetal head between prelabor and the second stage of labor. A total of 27 pregnant women were examined with 3D MRI sequences before going into labor using a 1 Tesla open field MRI. Seven of these patients subsequently had another set of 3D MRI sequences during the second stage of labor. Volumes of 2D images were transformed into finite element 3D reconstructions. Polygonal meshes for each part of the fetal body were used to study fetal head molding and brain shape changes. Varying degrees of fetal head molding were present in the infants of all seven patients studied during the second phase of labor compared with the images acquired before birth. The cranial deformation, however, was no longer observed after birth in five out of the seven newborns, whose post-natal cranial parameters were identical to those measured before delivery. The changing shape of the fetal brain following the molding process and constraints on the brain tissue were observed in all the fetuses. Of the three fetuses presenting the greatest molding of the skull bones and brain shape deformation, two were delivered by cesarean-section (one after a forceps failure and one for engagement default), while the fetus presenting with the greatest skull molding and brain shape deformation was born physiologically. This study demonstrates the value of 3D MRI study with 3D finite element mesh reconstruction during the second stage of labor to reveal how the fetal brain is impacted by the molding of the cranial bones. Fetal head molding was systematically observed when the fetal head was engaged between the superior pelvic strait and the middle brim.
Humans have a pelvis that is less conducive to easy delivery of the large fetal head than other mammals. Factors related to a safe vaginal delivery include an adequately sized and shaped maternal bony pelvis, soft tissue shaping of the birth canal during delivery, sufficient uterine contractions, and a fetal head of the proper size and ability to mold. Labor dystocia most often results from a combination of these fetal and maternal factors. Even when vaginal delivery is possible, the birth process can be traumatic to the infant, with asymptomatic brain hemorrhages and retinal hemorrhages occurring in up to 43% of vaginally delivered neonates .
Seven pregnant women were examined with 3D MRI before going into labor and during the second stage of labor . This prospective biomedical observational study (IMAGINAITRE) was approved by the French ethical Institutional Review Board “Ile de France II” (ID-RCB 2012-A01469-34) and by the French National Agency for Drug and Medical Product Safety (Agence Nationale de Sécurité du Médicament et des Produits de Santé) and promoted by the University of Clermont-Ferrand Medical Center. All the women agreed to participate and signed an informed consent.
This study demonstrates the value of 3D MRI assessment using 3D finite elements mesh reconstruction during the second stage of labor to reveal how the fetal brain is impacted by the molding of the cranial bones. Fetal head molding was observed on MRI in all seven patients during the second phase of labor. The cranial deformation observed on MRI was not observed on clinical exam in five of the seven newborns. Overlapping of the cranial sutures was most marked in the anterior-posterior direction, at the coronal and lambdoid suture. These findings need to be confirmed in a larger series.