Πέμπτη, 28 Ιουνίου 2012

Human birth observed in real-time open magnetic resonance imaging


OBJECTIVE: Knowledge about the mechanism of labor is based on as- sumptions and radiographic studies performed decades ago. The goal of this study was to describe the relationship between the fetus and the pelvis as the fetus travels through the birth canal, using an open mag- netic resonance  imaging  (MRI) scanner. 
RESULTS: Delivery occurred  by progressive head extension.  However, extension was a very late movement that was observed whethe occiput was in close contact with the inferior margin of the symphysis pubis, occurring simultaneously with gliding downward of the fetal head.
CONCLUSION: This  observational  study  shows,  for  the  first  time, that birth can be analyzed with real-time  MRI. MRI technology allows assessment of maternal and fetal anatomy during labor and delivery.
 
Key words:  delivery, imaging, mechanism of labor, magnetic resonance imaging



Thorough understanding of maternal and fetal anatomy and physiology is essential for proper management of labor and delivery. The mechanism of labor is generally understood as the movements of the fetus in relation to the bony structures and soft tissues of the birth canal during labor. More than 1000 radiographic examinations of the pelvis and fetal head before, during, and after labor were performed in early studies to better understand the mechanism of birth.1-3   However, prenatal x-ray expo- sure  has  been  associated  with  an  increased risk of childhood cancer in case- control studies.4-6 
Nonionizing radiation is preferable in pregnant women. Numerous trials of magnetic resonance imaging (MRI) have not revealed any experimental or clinical evidence of fetal harm7-10;  thus, MRI is considered safe for the mother and fe- tus.11,12 MRI has been used to elucidate fetal anatomy,13-16 placental morphol- ogy,17 amniotic fluid volume,18  and bio- chemical assessment (ie, magnetic reso- nance spectroscopy).19  Furthermore, MRI pelvimetry used to be performed to predict consistently women at risk for cephalopelvic disproportion.20-23 Open-configuration MRI systems were de- signed to facilitate interventional proce- dures and functional MRI examinations and to increase patient comfort.24 A field strength of 1 Tesla or more is desirable for obtaining high-quality images in open MRI systems.
Ultrasound is increasingly used to doc- ument fetal head position and station within the maternal pelvis at various stages of labor,25-31 but it also has some limitations. We used an open MRI scanner ttake images of a human delivery. Our main
goal was to describe the relationship be- tween fetal movements and positio
as the fetus passage through the birth canal, using an open MRI scanner.




MATERIA L AN D METHOD S
We designed the observational study to
maximize safety for the mother and fetus. Rupture of the amniotic membranes was not planned in early labor because it was suggested previously that the amniotic fluid could lower the intrauterine acoustic sound pressure by 30 dB.32 This is enough to reduce acoustic sound pressure to an ac- ceptable level (<90 dB). In the late second stage, as the fetal head extended and thperineum distended, cinematic MRI a quisition was terminated to ensure that the ears of the newborn were still covered by maternal soft tissue, thereby avoiding ex- posure to MRI noise. During the delivery a midwife (G.R.) and an obstetrician (C.B.) stayed in the magnet room (Figure 1). There were 2 screens inside, 1 to monitor the fetal heart tracing and the second to observe the MRI images. A neonatologist and an anesthetist were also asked to be present in the magnet room. If there had been an abnormal labor course or an emergency, we would have been able to in- terrupt the MRI birth immediately and transfer to the delivery unit. The MRI suite and the delivery unit are on the same floor, and the distance between them is less than

50 m.
The patient underwent intermittent elec- tronic fetal heart monitoring with a proto- type of a MRI-compatible telemetric system with the exception of the image acquisition time. This MRI-compatible wireless elec- tronic fetal heart rate monitoring prototype system, developed by us and modified from the Philips Avalon Cordless Transducer Sys- tem (Philips Healthcare, Best, The Nether-
 
 
Figure 1: Photograph of the open MRI scanner with the patient and the health care personnel before delivery 

 


lands), allows for continuous cardiotoco- graph tracing with few artifacts. MRI was performed on a 1.0 Tesla open high-field MRI scanner with vertical field orientation (Panorama; Philips Healthcare) using a BodySP-Xl receiver coil.
A T2-weighted multislice turbospin echo (TSE) single-shot sequence was used to visualize the midsagittal, coronal, and axial planes with the following settings:
1000 milliseconds time of repetition (TR),
100 milliseconds time of echo (TE), flip angle 90°, 40 slices of 6 mm with 1 mm gap, voxel size 1.4 X 1.6 mm, field of view (FOV) 300 X 262 mm, with constant level appearance (CLEAR) correction. The se- quences were repeated every 10 minutes during the second stage of labor. Real-time cinematic MRI series were acquired from the midsagittal plane for representation of the extension phase using an interactive TSE single-shot sequence (TR 1600 milli- seconds, TE 150 milliseconds, flip angle
90°, single slice of 6 mm, voxel size 1.4 X
1.5 mm, FOV 380 X 285 mm, with CLEAR
correction).


RESULT S

In November 2010, a 24 year woman at 37 5/7 weeks of gestation was admitted with regular con- tractions to the Department of Obstet- rics of the Charité University Hospital in Berlin, Germany. The patient received an epidural and was transferred to the open MRI suite. In addition, the cervix was fully dilated, and the presenting part was engaged. Eight MRI studies were performed over a period of 45 minutes: 7 antepartum studies (Figure 2) and 1 postpartum study. First, the woman was examined in the supine position with legs outstretched. In the active second stage, when the mother began expulsive efforts with the valsalva manoeuver, her legs were slightly abducted and sup- ported by padding. This period was eval- uated by real-time cinematic MRI series (Video Clip).
A 2585 gram appropriate-for-gesta- tional age boy with Apgar scores of 9, 9, and 10 at 1, 5, and 10 minutes. Umbilical artery and umbilical vein pH measure- ments are routinely assessed as part of our daily practice. However, because of technical difficulties with the umbilical artery blood sample in this case, only the umbilical vein pH was available, which was 7.32. A neonatologist assessed the condition of the baby. Immediately after childbirth, the maternal anatomy was imaged before and after expulsion of the placenta, using a BFFE sequence (Figure
3). The total individual study time in the magnet room was less than 1 hour. The woman tolerated the discomfort during labor well and her postpartum course was uneventful. She was discharged with her newborn 2 days after delivery. The pediatric screening examinations, in- cluding auditory tests, did not reveal any abnormalities.


Figure 2:View of the midsagittal MRI plane of the maternal pelvis before the expulsion phase without pushing




Figure 3: MRI examination of the maternal pelvis in the third stage of labor



COMMENTS
The mechanical factors that  influence the progress of labor are of interest to obstetricians, but they are often difficult to investigate. For many years, digital ex- amination was the only method that was used during labor to provide information about the mother’s bony pelvis and soft tis- sue and the fetus. This method has the dis- advantage that only limited areas of the fe- tus and birth canal can be assessed.
Because mechanical factors are pri- marily involved in the seven cardinal movements of labor33,34 (engagement, descent, flexion, internal rotation, exten- sion, external rotation, and expulsion) elucidation of the process of labor was also investigated by experimental studies on preserved pelvises and pelvic models. Anatomically correct models are imper-
ative for accurate simulations of normal and complicated deliveries.
Clearly, it is impossible to faithfully re- produce labor conditions in experiments involving models; therefore, conclusions based on the results of such studies remain hypothetical.35  In other words, it is diffi- cult to generate models that mirror accu- rately the in vivo relationships during the labor and delivery process, and hence, re- sults derived from simulation are often based on untested assumptions.
Ultrasound is the imaging modality of choice for pregnant women.36 Today the cardinal movements can be studied with sonography.37-40   Transperineal ultrasound is rapidly becoming an established method to assess progression of labor and the likelihood of a successful opera- tive vaginal delivery.41 However, specific bony landmarks of the maternal pelvis, such as the ischial spines, cannot be visu- alized by intrapartum ultrasound.25 Furthermore, it is impossible to evaluate the fetal attitude which is described as the degree of flexion or extension of the fetal


head in relation to the fetal spine34  because the fetal cervical spine is not visible by transperineal ultrasound.
Fetal MRI has become more widely available and has become an accepted and powerful complementary method for evaluation of the fetus.13  MRI can help to increase knowledge about mater- nal and fetal anatomy during labor. Bony structures as well as soft tissue could be assessed in great detail. MRI sequences of the birth process should be as quite as possible and resistant to movement arte- facts. Our preliminary experiments con- firmed the single-shot TSE sequence to be well suited for fetal imaging for these tasks; sequence optimization also aimed at minimizing the sound pressure level, which was given by the scanner in the range of 10.5–11.3 dB (Table).

Attitude-fetal  flexion or extension
In 1913, the German obstetrician Hugo Sellheim42  found that extension of the fetal head takes place after impingement of the suboccipital region of the fetal heaon the mother’s symphysis. This was thought to be caused by rotation around a transverse axis running through the lower border of the symphysis, resulting in de- flexion of the fetal head at the atlantooccipital joint and extension of the cervical spine. This movement begins before crowning. In 1957, the radiological inves- tigations of Borell and Fernström43,44 sug- gested that Sellheim’s explanation of the extension was incorrect. Borell and Fern- ström suggested that the fetal head is flexed and glides continuously downward. The thoracic and cervical spine undergoes ex- tension during the last stage of labor, whereas the fetal head remains flexed until after expulsion. Furthermore, they stated that there is a relatively large distance be- tween the head and the lower border of the symphysis.
An intermediate position between these 2 theories was developed by Murray (1890)45  and Jones (1906).46  The view of Murray45  was that the head continues to glide downward at the same time as thmovement of extension. According to Jones,46  the movement of extension does not occur merely at the articulation be- tween the occiput and the atlas but is pre- ceded by an extension of the entire cervical spine.
Our visualization of the normal mechanism of late second-stage labor by MRI shows that extension started as soon as the occiput was in close contact with the inferior margin of the symphysis pubis. Thereafter, extension was simultaneous with gliding downward of the fetal head. At this point, the birth canal curved 90° upward and the fetal head was delivered by extension and rotated around the symphysis pubis. To the best of our knowledge, this is the first time that this mechanism has been clearly visualized. Thus, our investigation of the mecha- nism of labor using real time MRI pro- duced results that are in line with Mur- ray’s and Jones’s theory, which were described more than a century ago.45,46

MRI-compatible cardiotocography Poutamo et al47 published a comparison of electronic fetal heart monitoring before and after MR imaging in 16 preg- nant women. The authors showed that MRI acquisition does not influence the fetal heart rate or fetal activity. Shake- speare et al48 and Vadeyar et al49 were the first to assess fetal well-being during MRI examination. They had to remove ferro- magnetic parts from the device to be able to use within the MRI scanner. These au- thors also found no visible effect of MRI on fetal heart rate patterns. In the present observation, the same approach regarding the cardiotocography was chosen, namely removing ferromagnetic parts to allow monitoring of fetal heart rate during MRI examination without interference.



Future research
Future research should include visual- ization of the first stage of labor by MRI. Arrest of labor, necessitating a cesarean delivery, is a major cause of maternal morbidity and mortality.50,51  An im- proved understanding of the mechanism of labor will help clinicians towards a more individualized approach to labor, allowing them to more easily distinguish normal and abnormal courses of labor. This knowledge would allow clinicians to intervene in a timely and effective fashion to ensure a favorable outcome. Furthermore, a basic knowledge of the attitude of the fetal head at the time of its passage through the lower part of the birth canal is of practical value in opera- tive vaginal deliveries. Future studies might also provide a basis for virtual re- ality computer programs to teach health care personnel in training.
The shape and direction of the birth canal has generally been investigated by palpation during labor and in frozen sec- tions from women who died during la- bor. There is no doubt that the human fetuses must negotiate a curve to be born.33  Nevertheless, there are conflict- ing results about the level of the curved part of the birth canal, the so-called knee. It is widely reported in textbooks, but not supported by evidence, that the knee lies at the level of the ischial spines.52  In contrast, Borell and Fernström1 stated that the curve of the birth canal lies lower and outside the bony pelvis and is entirely formed by the soft parts. MRI visualization of the ischial spine level during labor in comparison with the fetal head station during the extension phase may help to shed more light on this discussion.
In conclusion, collecting images of the fetus during delivery using an open MRI is feasible. We showed that MRI technol- ogy is useful for visualizing normal ma- ternal and fetal anatomy during labor. This observation opened a new way to study the mechanism of birth.              



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