Patent Publication Number: US-2006015036-A1

Title: Method and apparatus for monitoring the progress of labor

Description:
FIELD AND BACKGROUND OF THE INVENTION  
      The present invention relates to a method and apparatus for monitoring the progress of labor during childbirth.  
      Normal labor is generally divided into three stages: the first stage begins with the onset of labor and ends when dilatation of the cervix is complete; the second stage begins at that point and ends with the complete birth of the baby; and this is followed by the third stage which ends with the delivery of the placenta. During labor it is common to use either an external ultrasonic system for recording the baby&#39;s heart rate, and an external system for detecting the mothers uterine contractions, or an electronic system to sense the baby&#39;s heart pulses by an electrode attached to the baby&#39;s head and the mother&#39;s contractions by a pressure catheter applied to the mother inside the uterus.  
      However, a number of other physiological conditions of the mother and baby during labor can also be monitored in order to determine the progress of labor. These additional conditions include: (1) effacement (the thinning out of the cervix that occurs before and during the first stage of labor); (2) cervical dilatation (the increase in size of the cervical opening); (3) position of the cervix (the relation of the cervix to the vaginal axis, normally the fetal head); (4) station (the level of a predetermined point of the fetal presenting part with reference to the mother&#39;s pelvis), (5) position of the head which describes the relationship of the head to the pelvis and (6) and presentation which describes the part of the fetus (such as brow, face or breech) at the cervical opening.  
      The more common determination of station is the distance between the tip of the fetal head and the ischial spines which can be palpable by the physician; but a more accurate determination of station is the distance between the bi-parietal diameter (BPD) of the fetal head and the mother&#39;s pelvic inlet.  
      The foregoing conditions are generally determined by a physical examination, e.g., by the insertion of a finger through the mother&#39;s vagina. However, the accuracy of such a “finger” examination is very subjective and depends to a great extent on the experience, judgment, and even finger size, of the physician. Other drawbacks in such a physical examination are that it can be done only at spaced intervals, it generally produces discomfort to the mother, and it involves a number of risks including contamination, infection, dislodgment of a fetal monitor, injury to the baby, etc. Failure to interpret the precise stage of the labor progress from the physical examination can result in injury or even death of the baby or of the mother.  
      Many devices have been proposed in the past for automatically monitoring these conditions. As examples, U.S. Pat. No. 4,476,871 proposes an elongated tube having electrodes spaced along its length to monitor cervical dilatation during labor; U.S. Pat. Nos. 4,942,882 and 5,135,006 propose a fetal monitor probe attached to the fetal head to monitor heart beat, which probe is calibrated to monitor progress of descent; U.S. Pat. No. 5,222,485 proposes an elongated inflatable sac to monitor the position of the fetus and the configuration of the cervix; and U.S. Pat. No. 5,406,961 proposes a pessary to monitor the configuration of the cervix. However, for one reason or another, none of the previously proposed devices has come into any widespread use, and the historical “finger” examination continues to be the one in common use to this day.  
      Recent studies (Sherer et al., Ultrasound Obstet Gynecol 2002 March;19(3)):258-68) have demonstrated a high rate of error (75% and 65%) in transvaginal digital determination of fetal head position during active labor and the second stage of labor (respectively). The inaccurate assessment of the station or the position of the head also lead to decisions to use forceps or vacuum when the baby&#39;s head is too high in the birth canal, as well as delay in performing C-section when needed. In both cases the end result can be lethal to the fetus and highly damaging to the mother.  
      Moreover, the “digital (finger) test” can cause infections, and is forbidden in cases of early amniotic rupture. It also puts a heavy workload on the delivery room staff, particularly during peak periods. Furthermore, since the digital examination is intermittent, trends and sharp changes in the progress of labor are sometimes missed, again leading to potentially wrong decisions. Also, multiple digital examinations increase the risk of inflammation.  
      There is therefore a need for an apparatus and method to provide accurate information on the progress of labor.  
     SUMMARY OF THE INVENTION  
      According to one aspect of the present invention, there is provided a method of monitoring the progress of labor in a mother during childbirth, comprising: attaching a position sensor to a predetermined point on the mother&#39;s pelvic bones; monitoring the location of the position sensor in three-dimensional space relative to a reference; monitoring the location of the fetal presenting part with respect to the predetermined point on the mother&#39;s pelvic bones to provide an indication of the progress of labor; and measuring the cervical dilation by attaching sensors to the cervix.  
      In another embodiment of the present invention, there is provided a method of non-continuous monitoring of the progress of labor in a mother during childbirth, comprising: using a probe or finger-mounted sensor to measure the fetal presenting part relative to a predetermined point on the mother&#39;s pelvic bone, and to measure the cervical dilation by touching the cervix in, for example, two points.  
      Various embodiments of the invention are described below for purposes of example. In one embodiment, the location of the fetal presenting part, and also of the opposite sides of the end of the mother&#39;s uterine cervix, are monitored by position sensors attached to these respective elements. In a second described embodiment, the latter are monitored non-continuously using a hand held probe or finger-mounted sensor. In a third described embodiment, the latter are monitored by operating an ultrasonic transducer to image the mother&#39;s cervix and pelvic bones, and the fetal head, on a screen, and by using a position sensor on the ultrasonic transducer, and a marker for marking the screen, to locate the positions of these elements. A fourth embodiment is described utilizing at least two sensors, one of which is attached to a bony position on the pelvis to serve as the reference point, and the others may first be used to map the pelvis from outside of the body and to map the BPD plan by attaching it to the ultrasound probe, to map the ischial spines and ischial tuberosities from the inside and then to be attached to the cervix and fetal presenting part.  
      In a further embodiment of the present invention, position sensors may also be attached to, or position coordinates may be obtained of, the anterior superior iliac spine, the pubic symphysis, the scrum at 1-3 levels, the ischial spines and the ischial tuberosity, and such positions may be used for mapping the pelvic inlet outlet and midpelvis. Such mapping or pelvimetry may be helpful in determining whether the head of the baby is of suitable size for passage through the birth canal.  
      According to further features described in embodiments, the cervical dilatation of the mother&#39;s cervix is continuously indicated by monitoring the positions of the position sensors applied to the opposite sides of the end of the cervix, and continuously displaying the spatial distance between them. The position of the fetal presenting part (e.g., fetal head) is also continuously indicated by monitoring and displaying their respective locations.  
      In a second embodiment, the cervical dilatation of the mother&#39;s cervix and the position of the fetal presenting part or the BPD are monitored on a non-continuous basis by touching a probe or finger-mounted sensor to each side of the cervix and a pre-determined point or points on or connected to the fetal head.  
      According to further features in the described embodiments, the above conditions are computed and displayed in the form of units of distance (e.g., cm), and/or in the form of a graph, which may be called a partogram, showing the interrelation of the cervical dilatation and the descent of the fetal presenting part. Furthermore, such display may include an image of the fetus within the birth canal and the relation and orientation over time of the head to the pelvic inlet, outlet and midpelvis.  FIG. 4A  presents an illustration of a display of position of the presenting part in various stages of labor, in accordance with an embodiment of the present invention. Other methods to display such information may be used.  
      According to a further embodiment of the invention there is provided an apparatus for monitoring the progress of labor in a mother during childbirth, including: at least two sensors, one of which is attached to a bony position on the pelvis  8  to serve as the reference point, and another may first be used to map the pelvis from outside of the body, to map the BPD plan by attaching it to the ultrasound probe, to map the ischial spines and ischial tuberosities from the inside and then to be attached to the fetal presenting part, and may be attached to the sides of the cervix.  
      The output device is preferably a display, but could be a plotter, recorder, or other device for displaying, recording, and/or processing the data outputted by the computer  
      As will be described more particularly below, such a method and apparatus permits the progress of labor to be monitored in a manner which is either continuous or intermittent, which is less dependent for accuracy on the experience, judgment or finger size of the attendant in the conventional “finger examination”, which subjects the mother to less discomfort, and which involves less risk of contamination, infection, dislodgment of a fetal monitor, or injury to or death of the baby or mother due to a wrong assessment of the fetal position or of labor progress. Moreover, this technique enables more precise monitoring of the critical condition, namely the changes in the spatial distance of the BPD of the baby&#39;s head with respect to the pelvic inlet.  
      Further features and advantages of the invention will be apparent from the description below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:  
       FIG. 1  is a block diagram illustrating one embodiment of a system constructed in accordance with the present invention;  
       FIG. 2  illustrates one of the position sensors in the system of  FIG. 1 , according to an embodiment of the invention;  
       FIG. 3  is a block diagram of one type of position sensor system that may be used, according to an embodiment of the invention;  
       FIG. 4  more particularly illustrates the partogram display in the system of  FIG. 1 , according to an embodiment of the invention;  
       FIG. 4A  presents an illustration of a display of position of the presenting part in various stages of labor, in accordance with an embodiment of the present invention;  
       FIG. 5  is a block diagram illustrating an imaging system for displaying the image of the mother&#39;s womb, particularly the cervix, pelvic bones, and the fetal head to better show the progress of the labor, according to an embodiment of the invention;  
       FIGS. 6A-6D  illustrate displays produced by the system of  FIG. 5  during the various stages of labor, according to an embodiment of the invention;  
       FIG. 7  illustrates a display produced by the system of  FIG. 5  during the descent of the fetal head, according to an embodiment of the invention;  
       FIG. 8  illustrates how the monitored data may be processed to display the changes in the spatial distance of the BPD of the baby&#39;s head with respect to the mother&#39;s pelvic inlet, according to an embodiment of the invention;  
       FIG. 9  illustrates a fetal heart monitoring display and uterine contractions that may be included in an embodiment of the invention;  
       FIG. 10A  illustrates a finger mounted sensor in accordance with an embodiment of the present invention;  
       FIG. 10B  illustrates a close up view of an asymmetrical indentation from a finger mounted sensor and a corresponding protrusion on a sensor attached to the fetal head in accordance with an embodiment of the present invention;  
       FIG. 10C  illustrates an asymetrically shaped cover that may be attached to a fetal sensor in accordance with an embodiment of the present invention; and  
       FIG. 11  illustrates rigid members that can be attached to the cervix and fetal presenting part in accordance with an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      In the following description, various aspects of the present invention will be described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the present invention. However, it will also be appreciated by one skilled in the art that the present invention may be practiced without the specific details presented herein. Furthermore, well known features may be omitted or simplified in order not to obscure the present invention.  
      Referring to  FIG. 1 ,  FIG. 1  schematically illustrates an example of a mother&#39;s womb during labor and a system for monitoring the process. A computer  12  (which may be, for example, a personal computer, a workstation, a dedicated device including a “computer on a chip”, etc), inter alia, outputs displays, such as displays  14  or  16 , to, for example, a monitor. Displays other than those shown may be used. Computer  12  is operatively connected to, for example, a transmitter  10  and sensors PS. Transmitter  10  need not be used. Computer  12  typically includes appropriate software and one or more appropriate processors.  FIG. 1  depicts the fetus  2  in its normal position within the uterus  3  wherein the fetal head  4  is downwardly oriented in preparation for delivery via the cervix  5  of the uterus. The cervix  5  is dilated and effaced in preparation for passage of the fetus via the cervical canal and the vaginal cavity. The various stages of descent of the fetal head during delivery may be measured, for example, in relation to the ischial spines or the pelvic inlet  8   a  of the pelvic bones  8 .  
      The progress of labor is monitored by, for example, a set of position sensors attached to the fetal head and to the various parts of the mother&#39;s womb and pelvis, as follows: a first position sensor PS 1 , may be attached to, for example, one of the pelvic bones  8  as a reference point from the ischial spines and the pelvic inlet  8   a ; a second position sensor PS 2  may be attached to the fetal head  4  (or other typically presenting part of the unborn baby if not the fetal head); and third and fourth position sensors PS 3  and PS 4  may be attached to, for example, the opposite sides of the two ends of the external opening of the uterine cervix  5 A and  5 B. Attachment positions varying from those shown may be used.  
      In alternative embodiments, position sensor PS 2  may be attached to or made part of, for example, a fetal scalp electrode as are known in the art and as are commonly used in monitoring fetal life signs. For example, a position detection sensor PS 2  may be attached to or made part of a Copeland scalp electrode that attaches to the fetus with a hook, or to a fetal scalp electrode that attaches to a fetal presenting part with, for example, a screw, spring or spiral, etc.  
      In other embodiments, position sensor PS 2  may be attached to the fetal presenting part via other methods, such as with a suction cup, tape or other adhesive, etc.  
      A computer or monitor (e.g., computer  12  of  FIG. 5 , discussed below) can track movements of the pelvis, and thus can monitor the spatial position of the entire pelvis, particularly the pelvic inlet, outlet and midpelvis.  
      In certain embodiments, the position sensors PS 1 -PS 4  may be fixed in any suitable manner (e.g., by clips, suction cups, or other adhesives, etc.) to its respective surface. Each is typically capable of sensing its precise position and orientation in three-dimensional space with respect to a reference, as described in greater detail below. The position sensor may also be carried at one end of a rigid rod or object or other support which is clipped at its other end to the respective surface.  
      In an alternate embodiment of the present invention, the progress of labor is monitored on a non-continuous basis by a position sensor mounted on a hand held probe or on a thimble or other finger mount In one embodiment, a user&#39;s finger is used to manipulate the probe, and the finger has mounted on it a position sensor. The probe is touched to various points on the fetus and mother. The probe may also be, for example, mounted on a rod or other rigid object.  
      Reference is now made to  FIG. 10A  which illustrates a schematic diagram of a position probe or finger-mounted sensor  1000  in accordance with an embodiment of the present invention. Position probe or finger mounted sensor  1000  in the shape of, for example, a thimble, may fit over the distal end of a finger  1002  of the doctor or medical practitioner performing an examination. Other shapes and fits such as a ring or glove for holding such sensor are also possible. A lead or wire  1001  operably connects finger mounted sensor to a computer, processor or fetal monitoring station. Alternatively, the operable connection can be over a wireless electronic data link Sensor  1000  may operate similar to and may be used and incorporated into systems in a manner similar to probes PS discussed herein.  
       FIG. 10A  also depicts fetal presenting part  1004  such as a head or other part to which has been attached a fetal scalp orientation guide  1006 . Fetal scalp orientation guide  1006  may include appropriate electrodes, wires, or transmission devices (for, for example, transmitting heart rate information), or may not. Fetal scalp orientation guide  1006  may be fixed in any suitable manner (e.g., by clips, suction cups, or other adhesives, etc.) to its surface. Fetal scalp orientation guide  1006  may be attached to, may include, or may be made part of, for example, a fetal scalp electrode commonly used in monitoring fetal life signs; alternately fetal scalp orientation guide  1006  may not be associated with such devices. Fetal scalp orientation guide  1006  typically provides a reference or affixation point for contact with a position probe, and also provides an orientation guide for the position probe, by, typically, providing a key part or shape that forces, on appropriate contact with the position probe, the position probe (which includes a matching key part) to be oriented in a certain way with respect to the fetal scalp orientation guide  1006 . Scalp orientation guide  1006  is affixed to the fetus in an appropriate manner.  
      The distal end  1010  of finger mounted sensor  1000  may be fitted with one or more typically asymmetrically shaped protrusions  1012  that fits and matches the form of one or more indentation(s)  1009  located typically on the outward facing side  1008  of the fetal scalp orientation guide  1006 . Indentation(s)  1009  and protrusions  1012  each form a key part which matches the other part. The location of the protrusion(s)  1012  and indentation(s)  1009  may in other embodiments be alternated between the distal end  1010  of finger mounted sensor  1000  and the outward facing side  1008  of the fetal scalp orientation guide  1006 . The shape and number of the protrusion(s)  1012  and indentation(s) may vary from as shown. The “protrusions” or key part may not extend from the surface of the electrodes; for example the protrusions may be indentations allowing for a corresponding key-portion to be inserted or matched. Wires need not be used, and the position probes may operate according to wireless methods as discussed below.  
      In one embodiment of the present invention, in use, the probe or finger-mounted sensor  1000  may be touched to, for example, the fetal head  1004  (or other presenting part of the unborn baby) and to a set of points (wherein set may include one element) on the mother. Typically, the sensor  1000  is touched to each side of the external opening of the uterine cervix  1014 , but other parts of the mother may be used. Each side of the external opening of the uterine cervix  1014  may include key devices or guides for providing a reference or affixation point and orientation point, but typically no such device is needed on the mother. If such devices are used, they may be similar in shape to the guide  1006 .  
      In certain embodiments, the sensor may be touch-sensitive so that the touch of the sensor such as finger mounted sensor  1000  to the fetal presenting point  1004  or cervix triggers the calculation of the position of such points. In other embodiments, the examining physician may contact the finger mounted sensor  1000  with the designated point such as the fetal head, and may initiate position capture by indicating to a computer or monitoring device. For example, the user may click a mouse or operate a keyboard, foot pad or other switch which is operably connected to such position sensor to provide a user indication and to trigger the calculation of the position of the respective points. Reference or affixation points other than those shown may be used. The calculation of the relative position of the touched fetal presenting point  1004  relative to, for example, the opposite ends of the mother&#39;s uterine cervix  5 A and  5 B (or to other points) may permit the calculation of the progress of labor.  
      In certain embodiments, it may be desirable to collect more information than the touch of a finger-mounted sensor  1000  to a point on fetal presenting part  1004  provides to, for example, establish a required accuracy of orientation of the touched spot relative to the pelvic bones. Thus, in order to calculate the position of the fetal presenting part, it may be desirable to fix the orientation of the touch of the sensor  1000  to the fetal presenting part  1004 .  
      Reference is made to  FIG. 10B  which illustrates a close up view of an asymmetrical indentation protrusion(s)  1012  on a finger mounted sensor  1000  and a corresponding protrusion  1008  on a fetal scalp orientation guide  1006  in accordance with an embodiment of the present invention. Protrusions  1012  and  1008  typically provide a key system to, when in contact, fix their relative positions and orientations. A fixed orientation of the touch of the sensor  1000  to the fetal scalp orientation guide  1006  may be achieved by, for example, requiring that at the time of the calculation of the position of the sensor  1000  (e.g., the time of the click of the mouse as described above) protrusion(s)  1012  at the distal end  1010  of sensor  1000  is fitted onto the indentation(s)  1009  on the outward facing side of fetal scalp orientation guide  1006 . Typically, the protrusions require that when the sensor  1000  and orientation guide  1006  are in full contact, they have a specific relative orientation to each other.  
      Alternatively, the orientation of the touch of sensor  1000  on fetal presenting part  1004  may be determined by, for example, touching several (typically three, although other numbers may be used) designated points on fetal presenting part  1004  or on fetal scalp orientation guide  1006 . Such designated points could be, for example, any of three anatomical landmarks on the fetal head, such as the anterior and/or posterior fontanels, or three stickers or markers attached to the fetal presenting part  1004 .  
      Reference is made to  FIG. 10C  which illustrates a cap or covering  1016  that may be attached to fetal scalp orientation guide  1006  onto which is etched or attached an asymmetrically shaped form  1018  in accordance with an embodiment of the present invention. Other suitable forms, markings or shapes may be used. Establishing the orientation of the touch of sensor  1000  relative to fetal presenting part  1004  may be achieved by, for example, touching sensor  1000  to several (typically three, although other numbers may be used) points on asymmetrically shaped form  1018 . Such three points can be in the form of, for example, an non-isosceles triangle of points  1020 A,  1020 B and  1020 C which may be affixed or etched into fetal scalp orientation guide  1006 . Other shapes can be used. In certain embodiments the cap may be omitted. In certain embodiments, asymmetrically shaped form  1018  can be etched into or attached directly onto fetal scalp orientation guide  1006  or onto other sensors attached to the fetus.  
      In other embodiments, a first end of several (typically three, although other numbers may be used) rigid members of known length can be attached to each of the two ends of the cervix  5 A and  5 B and the fetal presenting part  1004 . A second end of each of such rigid members may be attached to, for example, a position sensor. Position and orientation of the cervix or the fetal presenting part cause the position of the sensors to change. In an alternative embodiment, the second end of such rigid members may be rotatably and moveably connected to a receptacle located outside of the body. Reference is hereby made to  FIG. 11  which illustrates rigid members  1102 , the first ends of which can be attached to, for example, the cervix  5 A and  5 B and fetal presenting part  1004  in accordance with an embodiment of the present invention. Other suitable attachment points, and other numbers of members, may be used. The second ends of such rigid members  1102  are movably inserted into, for example, a receptacle  1104  which measures the movement and orientation of such members  1102 . Such movement of the members  1102  reflects the dilation and effacement of the cervix  5 A and  5 B and the station and position of the fetal presenting part  1004 , and may record by, for example, an electronic, mechanical, or optical reader located within receptacle  1104  and attached to each of the rigid members  1102 . Receptacle  1104  may also have a position sensor as a reference point of the orientation of receptacle  1104  so that the position of rigid members is known relative to the position or receptacle  1104 .  
      Position sensors may be, for example, magnetic, ultrasonic, mechanical, inertial, fiber-optic or other known position sensors. Many types of position sensors are known for this purpose. In the illustrated example, position sensors PS 1 -PS 4  and sensor  1000  are of the magnetic field type as described, for example, in U.S. Pat. No. 4,945,305 to Blood. Other position sensors and methods of computing positions from sensors may be used. The position sensors PS or sensor  1000  may, for example, output signals, when triggered by, for example a transmitter  10  ( FIG. 1 ), enabling the precise position of the sensor to be computed by a computer  12  ( FIG. 1 ) connected to receive the outputs of the position sensors as well as the signals transmitted by the transmitter  10 . Computer  12  may compute the precise position and orientation of each sensor  1000  or sensor PS 1 -PS 4 , and from these computations, create and control displays for example those shown as  14  ( FIG. 1 ) and  16  ( FIG. 1 ), for displaying various physiological conditions of the mother and baby during labor, particularly the following (other conditions or sets of conditions may be presented):  
      1. Effacement  14 A: This is the process of thinning out the cervix that takes place before and during the first stage of labor. The cervix is thinned by retraction in order to allow more room for the birth process. Effacement may be expressed as a percent, from zero percent (uneffaced) to one hundred percent (cervix less than about 0.25 cm thick). In the system illustrated in  FIG. 1 , effacement is computed and displayed at  14   a  as the spatial distance between position sensor PS 2  attached to the fetal head and the middle point on the line connecting the two position sensors PS 3 , PS 4  attached to the ends of the uterine cervix  5 . Positions of sensor  1000  at various points may also be used for such calculations. Other methods of defining or presenting effacement may be used.  
      2. Cervical dilatation  14 B: This is the enlargement of the cervical opening. It is considered to be fully dilated when its diameter measures 10 cm since the fetal head of a term-sized infant usually can pass through a cervical opening of that diameter. In the system illustrated in  FIG. 1 , the cervical dilatation is computed and displayed at  14   b  as the spatial distance between the two position sensors PS 3 , PS 4 , attached to the opposite sides of the uterine cervix  5 . The position of sensor  1000  at suitable points may also be used for such calculations. Other methods of defining or presenting cervical dilatation may be used.  
      3. Position of the cervix  14 C: This is the forward-backward inclination of the cervix. In this case it is measured as the orientation of the central axis of the cervix, which is the line connecting the position sensor PS 2 , attached to the presenting part of the fetus, and the middle point on the line connecting the two position sensors PS 3 , PS 4  attached to the opposite sides of the cervix. An initial orientation of that cervical axis may be taken at the beginning of labor, and the progress of the cervical position is indicated as the relative angle between the cervical axis at any given time to the angle of initial orientation. The physician may designate any angular range as, for example, “forward”, or “middle”, or “backward”. Alternatively, the cervical position may be indicated as the distance between the symphys pubis, as determined by position sensor PS 1 , and the middle point of the line connecting the two position sensors PS 3 , PS 4  attached to the opposite sides of the cervix. Other methods of defining or presenting cervix position may be used. For example, the position of sensor  1000  at various points may also be used.  
      4. Station  14 D: This is the position of the fetal head (or other presenting part) with respect to a predetermined point of the mother&#39;s pelvis. As indicated earlier, the conventional station is the distance between the tip of the fetal head and the ischial spines. In one embodiment, a more accurate way of measuring the station may be used: to measure the distance between the BPD and the pelvic inlet. In the systems illustrated herein, the station may be computed and displayed in the conventional manner, based on the distance between the tip of the fetal head and the ischial spines as illustrated in  FIG. 7 , or in the more accurate manner based on the spatial distance of the BPD to the pelvic inlet as illustrated in  FIG. 8 . Other methods of defining or presenting such position may be used.  
      5. Position of the head which describes the relationship of the head to the pelvis, and presentation which describes the part of the fetus (such as brow, face or breech) at the cervical opening. Other methods of defining or presenting such position may be used.  
      6. Pelvimetry: This is the mapping or calculating of the area and shape of the pelvic inlet and pelvic outlet and midpelvis as are known in the art. A purpose of such mapping may be to determine whether the area of the pelvic inlet, outlet and midpelvis is suitable for passage of the baby. Other methods of defining or presenting such areas and shapes may be used.  
      The present invention may in certain embodiments provide a method of obtaining increased accuracy of pelvimetry. Such pelvimetry may be obtained by initially attaching or touching a sensor to some or all of the bony pelvis and the spine, and to some or all of the following spots in the mapping stage: the anterior superior iliac spines, pubic symphysis, the sacrum at 1-3 levels as may be measured externally or through the vagina, the ischial spines and the ischial tuberosity. Other measurement areas or sets of measurement areas may be used. Pelvimetry may be performed by embodiments of the present invention during active labor, before the onset of such labor, or at any other time  
      The position sensors PS 1 -PS 4  or 1000 may be of various known types.  FIG. 2  schematically illustrates one of such position sensors PS or 1000. It includes a, for example, triangular array of several (typically three, although other numbers may be used) spaced-apart magnetic coils  21 ,  22 ,  23 , all at precisely known distances from the center point  24  of the position sensor. Thus, by determining the positions and orientations of the three coils  21 - 23  with respect to a reference, the precise location of the center point  24  of the position sensor PS or  1000  can be determined with respect to that reference.  
      An example of a position sensor system which could be used with various embodiments is that described in Blood U.S. Pat. No. 4,945,305. Such a system, illustrated in the block diagram of  FIG. 3 , is capable of precisely measuring the position (location and orientation) in six degrees of freedom of receiving antenna  30  with respect to transmitting antenna  31  utilizing pulsed DC magnetic signals. The transmitting and receiving components consist of two or more transmitting antennas of known locations and orientation with respect to each other. The transmitting antennas  31  are driven one at a time (by a pulsed, direct current signal) from a DC drive circuit  32 . The receiving antenna  30  measures the transmitted direct current magnetic fields and the earth magnetic field in a signal processing circuit  33  and feeds this information to a computer  34  which thereby determines the position of the receiver antenna  30 . The computational processes taught by Blood may be used with various embodiments of the system and method of the present invention, and, for example, may be embodied in the computer  12  and/or software within the computer  12 . Other methods of computation may be used.  
      Further details of the construction and operation of such a position sensor system are set forth in U.S. Pat. No. 4,945,305, which is hereby incorporated by reference in its entirety. Other magnetic field systems which may be used with embodiments of the present invention may be, for example, based on AC fields, such as described in the patents set forth in the discussion of the prior art in the Blood patent.  
      Other position sensing systems that could be used for the position sensors PS 1 -PS 4  or 1000 are, for example, those produced by Polhemus Inc. or by Ascension Technology Corporation, both of Burlington, Vt., USA. In such systems, for example three mutually perpendicular magnetic fields are transmitted in sequence, and for example three mutually perpendicular directional coils are employed to detect the several magnetic fields. A computer is employed to compute the spatial position and orientation of the combined coils.  
      A still further position sensing system that could be used is that produced by Adaptive Optics Associates, Inc., of Cambridge, Mass., USA. This includes multiple light sources attached to the object whose position and orientation is to be detected, and a multiplicity of cameras positioned in known spatial locations to detect the light emitted by the light sources. A computer combines all the data and computes the position and orientation of the object.  
      Yet another position sensor system that could be used is that of Science Accessories Corporation of New Haven, Conn., USA. It includes an ultrasound source attached to the point on the object whose position is to be detected, and a multiplicity of microphones positioned in known spatial locations to detect the sound emitted by the ultrasound source. A computer combines the data and computes the position of the object By attaching multiple spaced-apart ultrasound emitters of the object, its orientation can also be computed by combining the position data of each of the emitters.  
      In one embodiment, the position sensors are of the wireless type so as to minimize interference with the birth process. In some cases it may be advantageous to use a mechanical positioning system based on robotic arms physically connected to the tracked objects and equipped with mechanical sensors at the joints (e.g., rotary encoders) which enable precise spatial location of the tracked objects.  
      Computer  12  ( FIG. 1 ) which receives data corresponding to the positions of the position sensors PS 1 -PS 4  (or, in one embodiment, sensor  1000 ,  FIG. 10 ), processes this data to provide the type of display that may be desired. Computer  12  may include software, memory, mass storage, a central processor (CPU), etc.  FIG. 1  illustrates two types of displays  14 ,  16 ; other displays may be used. Display  14  displays each parameter, effacement, cervical dilation, cervix position, station and/or BPP distance, in the form of units of distance (e.g. cm). Display  16 , however, is a Partogram, in which the cervical dilatation and the station are displayed in graphical form as a function of time to show the interrelation of the cervical dilatation and the descent of the fetal head (or other presenting part) and in which the effacement and cervical position may also be similarly displayed.  
      The Partogram display  16 , which is more particularly illustrated in  FIG. 4 , is of value since it provides a visual display of the progress of labor and can be recorded if desired. By using the Partogram, a better determination can be made whether labor is progressing normally. “Alert” and “action” lines may be printed on the Partogram to provide a visible indication of whether labor is progressing normally or abnormally, and thereby to better alert the attending personnel to take prompt action if necessary. Such an “electronic Partogram” can also markedly reduce the number of prolonged labors, the rate of intraparum, post partum and early neonatal infections, the number of unnecessary interventions, and neonatal trauma due to wrong assessment of the fetal head. A partogram need not be used, and other types of partograms may be used.  
       FIG. 5  illustrates a monitoring system similar to that of  FIG. 1 , further equipped with an imaging system for imaging the womb area of the mother and for continuously displaying, for example, the mother&#39;s cervix, pelvic bones, and fetal head (or other presenting part). Other parts may be displayed.  
      The system of  FIG. 5  includes an ultrasonic transducer  40  for imaging the womb area, via the computer  12 , on an image display  42 . It also includes a position sensor PS 5  attached to the ultrasonic transducer  40 . Position sensor  1000  may also be used to capture position information for this embodiment Thus, any point in the image on display  42  may be selected by a marker device  43 , such as a mouse or touch screen, and its location fed into the computer  12  to identify the location of the respective point with respect to the location of position sensor PS 1  attached to the mother&#39;s pubic bones. Other devices, such as a keyboard, may effect the function of the marker device  43 . Other or additional locations may be mapped. With this information, the computer  12  can compute the various relationships displayed in displays  14  and  16  (for example), possibly obviating the need for the positions sensors PS 2 , PS 3  and PS 4 . The image displayed in display  42  may be used in the same manner for marking, for example, the BPD on the fetal head as illustrated in  FIG. 8 , thereby enabling particularly the spatial distance between the fetal BPD and the pelvic inlet to be computed and monitored. Other computations may be made. It will be appreciated that other reference points, other than the BPD or the tip of the fetus head, as well as any other point of the mother&#39;s pelvis, may be used as the reference points for monitoring the progress of the labor. This freedom may be desirable because of the variety of preferences among various physicians.  
      The imaging system illustrated in  FIG. 5  could also be used to, for example, provide a visual image of the various stages of labor, e.g., as illustrated in  FIGS. 6A-6D  showing the progressive dilatation and effacement of the cervix, or as illustrated in  FIGS. 7 and 8  showing the progressive descent of the fetal head tip through the various stations with respect to the ischial spines  7  ( FIG. 7 ) or mother&#39;s pelvic inlet ( FIG. 8 ). If the imaging system is used together with all five position sensors PS 1 -PS 5  illustrated in  FIG. 5 , the ultrasound imaging may be used only to measure the BPD at the beginning of labor or later. Other sets of position sensors, with other positions, and with other configurations, may be used. The computer  12  then determines the distance between the BPD and, for example, the tip of the fetal head, and thereafter it can use the position of the tip of the fetal head also to determine the BPD position. The ultrasound imaging may thereafter be used only for verification if desired. It can also be used to verify cervical dilatation and effacement  
      The system illustrated in  FIG. 5  may also be used for, for example, sensing contractions in the mother&#39;s uterus. During contractions, the fetal head moves slightly, and the dilatation also grows slightly, and after contractions, they both retract to their previous positions. By thus observing the dilatation and/or fetal head position as a function of time, the attending physician may discern the occurrence of contractions as well as the duration and strength of such contractions. In addition, by including a heart pulse sensor in the fetal head position sensor PS 2 , the physician may observe the relation of the fetal heart rate (FHR) in relation to the uterine contractions (UC), to show the relationship between the two as illustrated in  FIG. 9 . Computer  12  may be programmed to receive the above information from the various sensors and produce, in a monitor  45 , a display, for example, corresponding to the fetal heart rate (FHR) in relation to the uterine contractions (UC), as illustrated in  FIG. 9 . Such information is particularly desirable if the presence of complications is established or anticipated. Other analysis may be possible.  
      While separate displays are shown in the drawings, it will be appreciated that these displays could be in the form of windows on the same large computer display.  
      While the invention has been described with respect to several preferred embodiment, it will be appreciated that these are set forth merely for purposes of example, and that many other variations, modifications and applications of the invention may be made.