EUROP. J. OBSTET. GYNEC. REPROD. BIOL., 1977,7/6, 0 Elsevier/North-Holland Biomedical Press
369-372
Measuring the height of a cephalic presentation: an objective assessment of station D. Lewin, G. Sadoul and Th. Beuret Department
of Obstetrics and Gynecology,
Centre Hospitalier de Poissy, Lhiversitd Paris V, France
LEWIN, D., SADOUL, G. and BEURET, Th. (1977): Measuring the height of a cephalic presentation: an objective assessment of station. Europ. J. Obstet. Gynec. reprod. Biol., 716, 369-372. The authors have previously described a method of objectively assessing the height of the presentation, an ultrasonic echograph measuring the distance from the head to the sacral tip. They have now obtained 453 measurements made before and during labor; norms are given according to the clinical evaluation of the station. The usefulness of the method is discussed. It may make the Bishop’s score more precise, permit a more accurate check of trial of labor and help to recognize a low station correctly before an application of forceps. monitoring; station of the head; descent
where its axis is a straight line which cuts the pelvic floor close to the sacral tip (Fig. 1). In Figure 2 it is apparent that the progress of the descent is in direct relation to the distance of the
Introduction
Since there is a general need for objective measurements during labor which may usefully be added to the clinical findings, heart fetal sounds, uterine contractions and cervical opening have been successfully recorded. But the ‘objective partogram’ does not currently include the height of the presentation, even if some X-ray attempts to measure it have been made (Magnin, Naudin and Thoulon, 1975). Lewin, Sadoul and Sylvain-Leroy (1977b) have described a simple, noninvasive method using ultrasonic waves. The results of the application of this method are presented in the present paper.
Material and method
In summary, the method consists of measuring the height of the head in the upper part of the pelvis
Fig. 1. Axis of pelvis.
369
D. Lewin et al.: Measuring the height of cephalic presentation
Umbilicus \
Sacrum \ Probe
Fig. 4. Position of the probe and direction of the ultrasonic waves. Fig. 2. Descent according to Farabeuf and Varnier (1891).
fetal cranial circumference from the sacral tip. This distance is measured by ultrasonic echography in mode A. The probe is a transducer with an external diameter of 15 mm; it is easily placed and fixed on the skin near the sacral tip. An ordinary gel is interposed. The frequency used is 1.5 MHz. The authors have slightly adapted an echograph formerly used to measure the width of pieces of metal (Fig. 3). When the probe is correctly orientated, theoretically in the direction of the maternal umbilicus (Fig. 4) but with a great latitude, two main echoes are observed. One is fured, at a distance of 9 mm generally. This is the posterior echo of the sacrum. This point was assessed by perineal echotomography
(Lewin, Sadoul and Sylvain-Leroy, 1977a). The second one is dependent on the height of the fetal head. This is the ‘first’ cranial echo. The distance between the two echoes (Fig. 5) gives the distance between the head and the sacral tip, a correct scale having been established. It is possible to record the descent continuously. Since an electronic device which selects the echoes and draws curves is not yet available, the scope of the echograph is filmed and the record preserved in a magnetoscope. Retrospective curves can be drawn when it is desirable. Using a concomitant recording of the uterine contractions, it is possible to follow the evolution of the head during and between the con-
t S
Fig. 3. The echograph. simultaneous records.
On the left, a cardiotocograph
for
t h
Fig. 5. Observed echoes. s = echo of the sacral tip; h = fist echo of the head.
371
D. Lewin et al.: Measuring the height of cephalic presentation
tractions. 504 separated measurements and 112 continuous records are now available before and during labor. Although no actual attempt has been made, the measurement of the height of a breech presentation is probably not obtainable by this method, at ieast at its present stage of development. There was no contracted or abnormal pelvis in this series, and no cesarean section was performed for mechanical reasons.
Results
In each case tested, whatever the clinical station of the presenting head, the degree of dilatation, the state of the membranes, the parity, the mother’s weight or the infant’s weight, it was always possible to obtain a definite, distinctive echo of the head. The measurements have been made especially when the axis of the descending head is a straight line, approximately as far as station t2. 11 measurements are nevertheless available for stations +3 and +4, the distances obtained varying from
TABLE I
Stations clinically assessed cross-matched
with
heights measured Clinical values
No.
Height measured (mm) Range
Mean
SD
41
41-49
45.09
1.87
165
35-45
40.31
2.01
98
27-36
32.30
1.60
Estimated below Station +l and above Station +2
33
24-29
21.85
1.23
Station +2
23
21-25
22.39
0.94
Station -1 (fixed, unengaged) Station 0 (iust engaged) Station +l
(engaged, high)
(engaged, middle)
TABLE II
Floating heads
Measurement (mm)
No.
Primigravidae
Multigravidae
48 49 50 51 52 53 54 55 56 58 61 62 65
13 19 21 22 9 1 1 1 2 1 1 1 1
12 16 16 15 1 0 0 0 1 0 0 0 0
1 3 5 7 8 1 1 1 1 1 1 1 1
19 mm to 16 mm. We have never observed a figure below 16 mm. The measurements of the height are compared with the results of the clinical findings from station -1 to station t2. The definition of the stations conforms to French obstetric training (Table I). When the station is higher (-2 or above) the head is termed ‘floating’ and the different stations are not usually separated in French records. The measurements obtained in 93 patients before or at the onset of labor are detailed in Table II.
Comments
The anatomical definition of engagement is the entering of the inlet. Since there is no direct, practical means of locating both the inlet and the biparietal diameter, clinical criteria for engagement are lacking in accuracy. For Hugues (1972) these criteria are met when the presenting part : _ reaches the level of the ischial spines; _ covers three-quarters of the pubic symphysis; and _ covers two-thirds of the anterior surface of the sacrum. Normally correct training permits an accurate
312
D. Lewin et al,: Measuring the height of cephalic presentation
assessment of engagement. Of course, mistakes are unavoidable. Frequently two well-trained obstetricians disagree about engagement. A caput succedaneum, a cephalhematoma or an abnormal molding may explain some discrepancies. Direct objective assessment has remained an unsolved problem. Location of the biparietal diameter cannot be correctly assessed by the use of X-rays, since diameters in films are generally not the projection of the actual diameters of the skull. Stereoscopy is more accurate (Magnin et al., 1975). This is far from being generally adopted, ionizing radiations being used cautiously in such conditions. Ultrasonic echotomography displays the biparietal diameter. It also allows the location of the anteroposterior diameter of the inlet (Schams and Bretscher, 1975) but not of other diameters. Consequently, engagement cannot be assessed by echotomography alone. The method presented here assesses engagement indirectly. Since the echoes of caput succedaneum and cephalhematoma are not significant, engagement may be assessed more accurately than by clinical means. According to the present authors’ experience to date, engagement does not occur when the distance from the head to the sacral tip is greater than 45 mm. Conversely, when this distance is equal to or less than 40 mm the head is always engaged. A mobile or floating head at the onset of labor has a conventional prognostic importance, which was again stressed recently (Weekes and Flynn, 1975). The authors are now studying how the measurement of the distance from the head to the sacral tip may supply improved information about this important element in Bishop’s score. Although the present method seems to be especi-
ally useful for assessing engagement, it was also con sidered whether it might help to recognize a low station for a low forceps, since during the last period of the second stage of labor the axis of the pelvis is no longer a straight line. There were, however, a few attempts to measure the distance from the head to the sacral tip just before forceps application. Below a value of 22, no abnormal resistance was encountered. In one case a forceps was tried even though the distance was 28. Traction had to be excessive; in the event there was no damage to the mother or the child.
References Farabeuf, L.H. and Varnier,H. (1891): Introduction ri l’ktude ciinique et cila pratiqne des accouchements, p. 100. Steinheil, Paris. Hugues, E.C. (1972): Obstetric-Gynecologic Terminology, p. 381. Davis, Philadelphia. Lewin, D., Sadoul, G. and Sylvain-Leroy, B. (1977a): Perineal echotomography and objective cervimetry. Europ. J. Obstet. Gynec. reprod. Biol., 7, 101. Lewin, D., .Sadoul, G. and Sylvain-Leroy, B. (1977b): J. Gynk-ObstPt. Biol. Reprod. (in press). Magnin, P., Naudin, E.P. and Thoulon, J.M. (1975): Radiodiagnostic obstetrical, p. 193. Expansion Scientifique, Paris. Schams, H. and Bretscher, J. (1975): UltrasonographicDiagnosis in Obstetric and Gynecology, pp. 148-151. Springer, Berlin. Weekes, A.R.L. and Flynn, M.J. (1975): Engagement of fetal head in primigravidas and its relationship to duration of gestation and time of onset of labor. Brit. J. Obstet. Gynaec., 82, 7. Address for correspondence: Dr. D. Lewin, Service de Gynecologie-obstetrique, Centre Hospitalier, F-78303 PoissyCedex, France.
369-372
Measuring the height of a cephalic presentation: an objective assessment of station D. Lewin, G. Sadoul and Th. Beuret Department
of Obstetrics and Gynecology,
Centre Hospitalier de Poissy, Lhiversitd Paris V, France
LEWIN, D., SADOUL, G. and BEURET, Th. (1977): Measuring the height of a cephalic presentation: an objective assessment of station. Europ. J. Obstet. Gynec. reprod. Biol., 716, 369-372. The authors have previously described a method of objectively assessing the height of the presentation, an ultrasonic echograph measuring the distance from the head to the sacral tip. They have now obtained 453 measurements made before and during labor; norms are given according to the clinical evaluation of the station. The usefulness of the method is discussed. It may make the Bishop’s score more precise, permit a more accurate check of trial of labor and help to recognize a low station correctly before an application of forceps. monitoring; station of the head; descent
where its axis is a straight line which cuts the pelvic floor close to the sacral tip (Fig. 1). In Figure 2 it is apparent that the progress of the descent is in direct relation to the distance of the
Introduction
Since there is a general need for objective measurements during labor which may usefully be added to the clinical findings, heart fetal sounds, uterine contractions and cervical opening have been successfully recorded. But the ‘objective partogram’ does not currently include the height of the presentation, even if some X-ray attempts to measure it have been made (Magnin, Naudin and Thoulon, 1975). Lewin, Sadoul and Sylvain-Leroy (1977b) have described a simple, noninvasive method using ultrasonic waves. The results of the application of this method are presented in the present paper.
Material and method
In summary, the method consists of measuring the height of the head in the upper part of the pelvis
Fig. 1. Axis of pelvis.
369
D. Lewin et al.: Measuring the height of cephalic presentation
Umbilicus \
Sacrum \ Probe
Fig. 4. Position of the probe and direction of the ultrasonic waves. Fig. 2. Descent according to Farabeuf and Varnier (1891).
fetal cranial circumference from the sacral tip. This distance is measured by ultrasonic echography in mode A. The probe is a transducer with an external diameter of 15 mm; it is easily placed and fixed on the skin near the sacral tip. An ordinary gel is interposed. The frequency used is 1.5 MHz. The authors have slightly adapted an echograph formerly used to measure the width of pieces of metal (Fig. 3). When the probe is correctly orientated, theoretically in the direction of the maternal umbilicus (Fig. 4) but with a great latitude, two main echoes are observed. One is fured, at a distance of 9 mm generally. This is the posterior echo of the sacrum. This point was assessed by perineal echotomography
(Lewin, Sadoul and Sylvain-Leroy, 1977a). The second one is dependent on the height of the fetal head. This is the ‘first’ cranial echo. The distance between the two echoes (Fig. 5) gives the distance between the head and the sacral tip, a correct scale having been established. It is possible to record the descent continuously. Since an electronic device which selects the echoes and draws curves is not yet available, the scope of the echograph is filmed and the record preserved in a magnetoscope. Retrospective curves can be drawn when it is desirable. Using a concomitant recording of the uterine contractions, it is possible to follow the evolution of the head during and between the con-
t S
Fig. 3. The echograph. simultaneous records.
On the left, a cardiotocograph
for
t h
Fig. 5. Observed echoes. s = echo of the sacral tip; h = fist echo of the head.
371
D. Lewin et al.: Measuring the height of cephalic presentation
tractions. 504 separated measurements and 112 continuous records are now available before and during labor. Although no actual attempt has been made, the measurement of the height of a breech presentation is probably not obtainable by this method, at ieast at its present stage of development. There was no contracted or abnormal pelvis in this series, and no cesarean section was performed for mechanical reasons.
Results
In each case tested, whatever the clinical station of the presenting head, the degree of dilatation, the state of the membranes, the parity, the mother’s weight or the infant’s weight, it was always possible to obtain a definite, distinctive echo of the head. The measurements have been made especially when the axis of the descending head is a straight line, approximately as far as station t2. 11 measurements are nevertheless available for stations +3 and +4, the distances obtained varying from
TABLE I
Stations clinically assessed cross-matched
with
heights measured Clinical values
No.
Height measured (mm) Range
Mean
SD
41
41-49
45.09
1.87
165
35-45
40.31
2.01
98
27-36
32.30
1.60
Estimated below Station +l and above Station +2
33
24-29
21.85
1.23
Station +2
23
21-25
22.39
0.94
Station -1 (fixed, unengaged) Station 0 (iust engaged) Station +l
(engaged, high)
(engaged, middle)
TABLE II
Floating heads
Measurement (mm)
No.
Primigravidae
Multigravidae
48 49 50 51 52 53 54 55 56 58 61 62 65
13 19 21 22 9 1 1 1 2 1 1 1 1
12 16 16 15 1 0 0 0 1 0 0 0 0
1 3 5 7 8 1 1 1 1 1 1 1 1
19 mm to 16 mm. We have never observed a figure below 16 mm. The measurements of the height are compared with the results of the clinical findings from station -1 to station t2. The definition of the stations conforms to French obstetric training (Table I). When the station is higher (-2 or above) the head is termed ‘floating’ and the different stations are not usually separated in French records. The measurements obtained in 93 patients before or at the onset of labor are detailed in Table II.
Comments
The anatomical definition of engagement is the entering of the inlet. Since there is no direct, practical means of locating both the inlet and the biparietal diameter, clinical criteria for engagement are lacking in accuracy. For Hugues (1972) these criteria are met when the presenting part : _ reaches the level of the ischial spines; _ covers three-quarters of the pubic symphysis; and _ covers two-thirds of the anterior surface of the sacrum. Normally correct training permits an accurate
312
D. Lewin et al,: Measuring the height of cephalic presentation
assessment of engagement. Of course, mistakes are unavoidable. Frequently two well-trained obstetricians disagree about engagement. A caput succedaneum, a cephalhematoma or an abnormal molding may explain some discrepancies. Direct objective assessment has remained an unsolved problem. Location of the biparietal diameter cannot be correctly assessed by the use of X-rays, since diameters in films are generally not the projection of the actual diameters of the skull. Stereoscopy is more accurate (Magnin et al., 1975). This is far from being generally adopted, ionizing radiations being used cautiously in such conditions. Ultrasonic echotomography displays the biparietal diameter. It also allows the location of the anteroposterior diameter of the inlet (Schams and Bretscher, 1975) but not of other diameters. Consequently, engagement cannot be assessed by echotomography alone. The method presented here assesses engagement indirectly. Since the echoes of caput succedaneum and cephalhematoma are not significant, engagement may be assessed more accurately than by clinical means. According to the present authors’ experience to date, engagement does not occur when the distance from the head to the sacral tip is greater than 45 mm. Conversely, when this distance is equal to or less than 40 mm the head is always engaged. A mobile or floating head at the onset of labor has a conventional prognostic importance, which was again stressed recently (Weekes and Flynn, 1975). The authors are now studying how the measurement of the distance from the head to the sacral tip may supply improved information about this important element in Bishop’s score. Although the present method seems to be especi-
ally useful for assessing engagement, it was also con sidered whether it might help to recognize a low station for a low forceps, since during the last period of the second stage of labor the axis of the pelvis is no longer a straight line. There were, however, a few attempts to measure the distance from the head to the sacral tip just before forceps application. Below a value of 22, no abnormal resistance was encountered. In one case a forceps was tried even though the distance was 28. Traction had to be excessive; in the event there was no damage to the mother or the child.
References Farabeuf, L.H. and Varnier,H. (1891): Introduction ri l’ktude ciinique et cila pratiqne des accouchements, p. 100. Steinheil, Paris. Hugues, E.C. (1972): Obstetric-Gynecologic Terminology, p. 381. Davis, Philadelphia. Lewin, D., Sadoul, G. and Sylvain-Leroy, B. (1977a): Perineal echotomography and objective cervimetry. Europ. J. Obstet. Gynec. reprod. Biol., 7, 101. Lewin, D., .Sadoul, G. and Sylvain-Leroy, B. (1977b): J. Gynk-ObstPt. Biol. Reprod. (in press). Magnin, P., Naudin, E.P. and Thoulon, J.M. (1975): Radiodiagnostic obstetrical, p. 193. Expansion Scientifique, Paris. Schams, H. and Bretscher, J. (1975): UltrasonographicDiagnosis in Obstetric and Gynecology, pp. 148-151. Springer, Berlin. Weekes, A.R.L. and Flynn, M.J. (1975): Engagement of fetal head in primigravidas and its relationship to duration of gestation and time of onset of labor. Brit. J. Obstet. Gynaec., 82, 7. Address for correspondence: Dr. D. Lewin, Service de Gynecologie-obstetrique, Centre Hospitalier, F-78303 PoissyCedex, France.
