Using Magnetic Resonance Imaging During Childbirth to Demonstrate Fetal Head Moldability and Brain Compression: Prospective Cohort Study

Abstract

Background: Childbirth is a physiological process with significant medical risk, given that neurological impairment due to the birthing process can occur at any time. Improvements in risk assessment and anticipatory interventions are constantly needed; however, the birthing process is difficult to assess using simple imaging technology because the maternal bony pelvis and fetal skeleton interfere with visualizing the soft tissues. Magnetic resonance imaging (MRI) is a noninvasive technique with no ionizing radiation that can monitor the biomechanics of the birthing process. However, the effective use of this modality requires teamwork and the implementation of the appropriate safeguards to achieve appropriate safety levels.

Objective: This study describes a clinically effective and safe method to perform real-time MRI during the birthing process. We reported the experience of our team as part of the IMAGINAITRE study protocol (France), which aimed to better understand the biomechanics of childbirth.

Methods: A total of 27 pregnant women were examined with 3D MRI sequences before going into labor using a 1-Tesla open-field MRI. Of these 27 patients, 7 (26%) 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 moldability and brain compression.

Results: All 7 observed babies showed a sugarloaf skull deformity and brain compression at the middle strait. The fetus showing the greatest degree of molding and brain shape deformation weighed 4525 g and was born spontaneously but also presented with a low Apgar score. In this case, observable brain shape deformation demonstrated that brain compression had occurred, and it was not necessarily well tolerated by the fetus. Depending on fetal head moldability, these observations suggest that cephalopelvic disproportion can result in either obstructed labor or major fetal head molding with brain compression.

Conclusions: This study suggests the presence of skull moldability as a confounding factor explaining why MRI, even with the best precision to measure radiological landmarks, fails to accurately predict the modality of childbirth. This introduces the fetal head compliance criterion as a way to better understand cephalopelvic disproportion mechanisms in obstetrics. MRI might be the best imaging technology by which to explore all combined aspects of cephalopelvic disproportion and achieve a better understanding of the underlying mechanisms of fetal head molding and moldability.

Keywords: cephalopelvic disproportion; fetus; magnetic resonance imaging; obstetrics; parturition.

Figure 1

(A) Open magnetic resonance imaging (MRI) room with sterile drapes and a delivering patient. (B) Patient in the open-field MRI after antenna installation and being positioned inside the magnetic field.

Figure 2

Patient installed in the open-field magnetic resonance imaging, with a gynecologist by her side.

Figure 3

(A) T2 gradient echo sequence showing an axial slice centered on the fetal brain at the superior inlet level. (B) The same sequence at the iliac bone level. (C) T1 gradient echo sequence in the sagittal plane showing bony pelvis and fetal head before entering into labor. The empty bladder is in retropubic position. (D) Same T1 gradient echo sequence showing the fetal head molding in the middle brim during second phase of labor with a full bladder. The fetal head is rotated in occipito-pubic position, and the full bladder is ascended above the upper limit of the pubic bone.

Figure 4

T2 dynamic imaging during maternal effort (successive images) at complete cervix dilation and unruptured membranes (dynamic acquisition). (A) Before maternal efforts: fetal head is above the sacro-pubic line. (B) Beginning of maternal efforts: the membranes start to change form to underline the vaginal route. (C) The intact membranes are approaching the superficial perineum level inside the vagina, the coccygeal bone is pushed posteriorly, the fetal head is under the superior limit of the pubic bone, and the bladder and the urinary sphincter are descending with the fetal head.

Figure 5

3D reconstruction and finite element meshing. (A) 2D image with mesh contouring. (B) Artifacted 3D mesh. (C) 3D volumes after optimization process.

Figure 6

3D fetal mesh in false colors (blue) showing the forces applied on the fetal head and their gradient (the greatest forces are displayed in hot colors) from left to right. (A) Head is above the superior inlet. (B) The fetal head is engaging at the superior brim with a contact of the occiput on the pubic bone. (C) The fetal head is engaging at the inferior brim and shows an important fetal head molding.