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Pelvic Shape and its Relation to Midplane Prognosis
PELVIC SHAPE AND ITS RELATION TO MIDPLANE PROGNOSIS D. FRANK KALTREIDER, M.D., BALTIMORE, Mn. (From the Department of ObstetricH, University of JJ!a.ryland Medical School)
HE relationship between the ability of a fetal head to surmount the brim T and the shape of the pelvic inlet has been recognized for years. The round-
ish, graceful, gynecoid pelvis accepts a fetal head best. More difficulty is experienced when the pelvis has anthropoid or platypelloid characteristics. The android pelvis probably causes the greatest inlet obstruction. Generally speaking, the pelvis that is more angular causes more difficulty at the inlet. What part the shape of the pelvis plays in midplane obstruction has not been emphasized. The funnel pelvis, which probably has android characteristics, has been recognized as especially dangerous, while the rachitic pelvis, with it!-! wide divergency from inlet to outlet, rarely causes difficulty after the inlet has been passed. During the course of study of the outcome of labor in patients in whom x-ray pelvimetry has been obtained, it was noted that pelvic shape definitely influenced the ability of the patient to deliver vaginally through the midplane. It is thought worth while to communicate this experience. :Material and Definitions
This study comprises 1,169 patients in whom x-ray pelvimetry was obtained during the period July 1, 1947, to July 1, 1950. Most of the x-rays were ohtained on patients with clinically suspect pelve~:>. Some x-rays were taken electively. These x-rays were read by both the x-ray department and the author. All pelves were classified by both the Department of Roentgenology and the author. The interspinous diameter ( I.S.) is defined as the shortest distance between the tips of the ischial spines. The anteroposterior diameter of the midplane (A.P.M.) is the distance between the lower portion of the symphysis pubis that is closest to the spines and the junction of the fourth and fifth sacral segments. The posterior sagittal of the midplane (P.S.M.) is defined as the distance hetween the I. S. diameter and the junction of the fourth and fifth sacral segments. Not all patients are included. All who had elective cesarean sections were deleted as well as patients having cesarean section for uterine inertia or inlet obstruction. Easy vaginal deliveries are those in which the patients delivered spontaneously or with forceps that did not require excessive traction. Difficult deliveries are those in which there was difficulty with rotations, when excessive traction was used, or when the baby showed evidence of intracranial injury or was stillborn because of the pelvis. Sections for midplane obstruction after trial of the midplane with labor are in the difficult group. Stillbirths from separation of the placenta, etc., were considered easy deliveries. Classification by X-ray
Table I shows how pelves are classified at various clinics throughout the United States and Great Britain. There is a moderate variation in interpreta116
Volume 63 :'\lumber I
RELATION OF PELVIC SHAPE TO MIDPLANE PROGNOSIS
117
tion. This may be due to differences in racial and economic factors. There is a moderate agreement with respect to gynecoid pelves, but the classification of other types varies considerably. I
TABLE
Sloane Hospital for Women1 Pettit, Garland, I>unn, Shumaker1 Javert, Steele, and Powlitis2 Walsh, John G.s Kenny, Meave4 Diekinson and Prooters
50.6
22.7
4.4
22.4
1.8
51.0
18.0
5.0
21.0
5.0
50.0
13.0
9.0
28.0
56.0 54.46 74.0
17.25 10.01 1.66
3.0 2.81 1.66
23.75 31.76 1.33
9.38 20.66
CLAS§IFICATIQa QF ~:l!!l;i- ElmBE liBI:lll! BASIC FORMS
448
39.0'4
118
Fig. 1.
This discrepancy was marked in our own clinic. Table II shows the lack of agreement in the same pelves between the Department of Roentgenology and the author. We agreed on both the anterior and posterior segments of the pelves in 44 per cent of the patients. We disagreed entirely in 23 per cent of the cases. We agreed on the posterior segment 57 per cent of the time and on the anterior segment 62 per eent of the time.
11 8
-----
---
J.
Ob:- 1. iX
(":;ynt'l
J .l nu :ll') ·. J <) C2
II.
CLM>8IHCATIO:" Ol' PEJ.Vb:; . Cow, ELA 'l'IO!\ (J!' INTEIU'H ET A'l'ION In: X -RAY :DEPAI:'l'MEK'r ANn Am'HOf:, .I ,149 P~; r , vEs ---------·---·- _______ __ .._______ -- - ----- ·-------
'l'ABLE -
:\ m .
KALTRBIDEl~
-- --- ---~ ---- --- ----------- -- ---- ----
·-·--
X-ray JJt:partm eut and At!tltor .dgret: on Classification oj' P dve.,
1. 2. 3. 4.
W{th botilaii teriOr- and posierior -~egmen ;:~------· --· .. - 'ii % -fi7 % With posterior segment of pelvi~ onl y ti:.! % With anterior segment of pelvis only No agreement ~~-~ith~_se~ent _ .. ___________ _____ _ :?~- ~ -- --- --· __
Fig. 1 shows how the author classified 1,149 pelves, according to their basic form, i.e., the posterior segment. Fig. 2 illustrates the classification of both segments. The total column represents the posterior segment, and the various divisions of the column represent the anterior segment. Note that this grouping does not agree to any extent with the various classifications found in Table I. At best the classification is based on visual impression and all of us obviously do not ''see'' alike. CLASSIFICATION OF PELVES- ENTIRE GROUP BASIC FORMS
448
39.0'X.
362
t9.2'X.
221
0-4-- -
Fig. 2. TABLE
III.
EASY RACE AND ECONOMIC STATUS
Negro White ward Private All ca.ses
I
ANDROID GYNECOID
%
70.2 80.0 79.6 74.7
F ACTOHS
RACIAL AND ECONOMIC
%
81.7 85.0 85.5 83.5
I
PLATY· PELLOID
%
83.4 80.0 84.6 83.3
JN DIFFICULTY OF DELIVERY DU'FICULT
I
ANTHROPOID
AKDROID
IGYNECOID
PLATYPELLOID
79.6 81.3 87.1 82.6
29.8 20.0 20.4 25.3
18.3 15.0 14.5 16.5
16.6 20.0 15.4 16.7
%
%
%
%
I ANTHROPOID %
20.4 18.7 12.9 17.4
Volume 63 Number I
RELATION OF PELVIC SHAPE TO MIDPLANE PROGNOSIS
119
Table III demonstrates the outcome of labor with respect to ease or difficulty in this series, according to pelvic shape and racial and economic factors. The android pelvis gave the most difficulty, while the remainder of the pelves had essentially the same outcome. This ease or difficulty refers to the pelvis as a whole and not to any one particular plane. CORRELATION OF I .S. AND A.P.M. DIAMETERS IN ALL PELVES 860 CASES ABOVE 9.00 M.
306 CASES
488 CASES
34 DIFFICULT
22 DIFFICULT
ILO% DIFFICULTY
4.5 'l:. DIFFICULTY
28 CASES
38 CASES
10 DIFFICULT
13 DIFFICULT
36 "4 DIFFICULTY
34% DIFFICULn
:t.s. 9.ooM. BELO w 9.0C M.
BELOW 12.0 CM
12.0 CM.
ABOVE 12.0CM.
A.P..M.
Fig. 3.
CORRELATION OF LS. AND P.S.M DIAMETERS IN All PELVES 860 CASES
ABOllE
389 CASES
406 CASES
37 DIFFICULT
18 DIFFICULT
9.5% DIFF ICULTV
4.5% DIFFICULTY
40 CASES
25 CASES
14 DIFFICULT
9 DIFFICULT
35 "/• Dl FF I CULTY
36% DIFFICULTY
9.0CM.
I.S. 9.0 CM.
BELOW 9.00M
BELOW 4.6 CM.
4.6CM. P.S.M.
ABOVE 4.6 CM.
Fig. 4.
The Midplane The transverse diameter of the midplane (I.S.) was correlated separately with the two A.P. diameters (A.P.lVL and the P.S.M.). This correlation was done by the use of seattergrams (Figs. 3 and 4). In order to find out what lengths of diameters may be considered borderline diameters, the scattergrams were divided arbitrarily into four quadrants. The percentage of difficult labors through the midplane was then calculated. These quadrants were varied in size by changing the lengths of the diameters at 0.2 em. levels. For example, in Fig. 3 the horizontal line was drawn at 9.4 em., and the vertical line was drawn at
KALTREIDER
120
Am.
J. Qb,t.
& Gynec. January, !952
11.4 em. The percentage of difficulty was then established in each quadrant. Both lines were then varied until there was the greatest difference in perrentage of difficulty in the large pelves (right upper quadrant) and the smallest pelves (left lower quadrant). In both graphs the I.S. of 9.0 em. was found to lw borderline, while the borderline A.P.M. was 12.0 ern. and P.S.l\I. 4.6 em. Jt was disturbing to note that in the large pelves (right upper quadrants of both figures) there was still difficulty of 4.5 per cent or 1 in 22. It was also noted that the length of the A.P. diameter was a factor when the I.S. diameter was CORRELATION OF I.S. AND A.P.M. DIAMETERS IN GYNECOID AND PLATYPELLOID PELVES 259 CASES 108 CASES
146 CASES
12 DIFF I CUI.. T
2 DIFFICULT
II t, DIFFICUI,. TY
1.4'4 DIFFICULTY
3 CASES
2 CASES
3 DIFFICULT
2 DIFFICULT
lOOt, DIFFICULTY
100'4 DIFFICULTY
ABOVE
9.0CM.
:r.s. 9.0 eM.
BELOW
9.0CM.
BELOW 12.0CM.
12.0CM.
ABOVE 12.0 CM.
A,P. M.
Fig. 5.
CORRELATION OF I.S. AND P.S.M. DIAMETERS IN GYNECOID AND PLATYPELLOID PELVES 256 CASES 121
128 CASES
CASES
ABOVE
9.0CM
II DIFFICULT
2 DIFFICULT
9'1:. DIFFICULTY
1.6'4 DIFFICULTY
6 CASES
I CASE
5 DIFFICULT
I DIFFICULT
83,. DIFFICULTY
100,. DIFFICULTY
I.S. 9.0CM.
BELOW
9.0CM.
BELOW 4.6CM.
4.6 CM. P.S.M.
ABOVE '1.6 CM.
Fig. 6.
of the longer variety. The difficulty was doubled when the A.P.M. was under 12.0 em. or the P.S.M. under 4.6 em. This did not hold true when the I.S. was 9.0 em. or below. Then the A.P. diameters did not appear to affect the outcome of labor. There was routinely 35 per cent difficulty when the I.S. diameter was 9.0 em. or below. Pelvic shape was considered next. Since the android pelvis is usually incriminated in midplane and outlet difficulty this group was removed 1 leaving
Volume 63 Number 1
RELATION OF PELVIC SHAPE TO MIDPLANE PROGNOSIS
121
the gynecoid, platypelloid, and anthropoid, both pure and mixed forms. There Wa.-3 no change in the amount of difficulty in the four quadrants of the scattergrams. The anthropoids were deleted next. No change noted. Finally any pelvis in which there were android or anthropoid characteristics, whether in the posterior segment or anterior segment, were deleted. Now there appeared to be a marked change (Figs. 5 and 6). Now the amount of difficulty in the larger pelves (right upper quadrant) was cut to one-third from 4.5 per cent to 1.5 per cent. There was no change in the relationship of pelves with longer LS. diameters and shorter A.P. diameters (left upper quadrant). There were very few pelves left with I.S. diameters of 9.0 em. or less, but this group was essentially 100 per cent difficult.
Comment Lilienfeld, Treptow, and Dixon6 have demonstrated that classifying pelves is not a simple procedure. Two different observers agreed on the classification of the anterior segment 52 per cent of the time and on the posterior segment 59 per cent of the time. There is apparently no uniformity in evaluation of shape by different observers. Even more important Lilienfeld and co-workers have shown that when one individual classifies a pelvis more than once he will not agree with himself more than 62 per cent of the time. For the above rea.<3ons the author is not sure that pelvic shape enters "into the picture" when evaluating the midplane. From my own interpretation of pelvic shape as seen in the x-ray it seems to be of definite help. Android and anthropoid characteristics in the midplane increase difficulty in larger pelves by 3 times, while gynecoid and platypelloid pelves with short I.S. diameters are dangerous. What the results would be, if another observer repeated this work, would be highly conjectural. It would seem worth while for it to be repeated. Conclusions 1. The classification of pelves by visual methods into gynecoid, anthropoid, platypelloid, and android is difficult. Consistency is lacking. 2. An I.S. of 9.0 em., A.P.M. of 12.0 em., and P.S.1VI. of 4.6 em. may he borderline in the midplane. 3. Patients with pelves of any shape may have difficulty in the midplane regardless of size; 4.5 per cent when the diameters are above border line; about 10 per cent when the I.S. is over border line and the A.P.M. or P.S.M. is below border line; and 35 per cent when the I.S. diameter is 9.0 em. or below. 4. Patients with gynecoid and platypelloid pelves and I.S. over 9.0 em., A.P.M. over 12.0 em. and P.S.M. over 4.6 em. will probably have little trouble. 5. An I.S. diameter of 9.0 em. or less may be more dangerous in the gynecoid and platypelloid pelves than in android and anthropoid pelves .
•
The author wishes to express his appreciation to the members of the Department of Roentgenology of the University of Maryland School of Medicine for their faithful and generous assistance in this study.
References 1. 2. 3. 4. 5. 6,
Caldwell, W. E., Moloy, H. C., and Swenson, P. C.: Am. J. Roentgenol. 41: 505, 1939. Javert, C. T- Steele, K. B., and Powlitis, M. E.: AM. J. 0BST. & GYNEC. 45: 216, 1943. Walsh, J. G.: AM:. J. OBsT. & GYNEC. 39: 255, 1940. Kenny, M.: J. Obst. & Gynaec. Brit. Emp. 51: 277, 1944. Dickinson, K., and Procter, I. M.: AM:. J. OBST. & GYNEC. 44: 585, 1942. Lilienfeld, A. M., Treptow, E., and Dixon. D. M.: Human Bioi. 21: 143, 1949,
HE relationship between the ability of a fetal head to surmount the brim T and the shape of the pelvic inlet has been recognized for years. The round-
ish, graceful, gynecoid pelvis accepts a fetal head best. More difficulty is experienced when the pelvis has anthropoid or platypelloid characteristics. The android pelvis probably causes the greatest inlet obstruction. Generally speaking, the pelvis that is more angular causes more difficulty at the inlet. What part the shape of the pelvis plays in midplane obstruction has not been emphasized. The funnel pelvis, which probably has android characteristics, has been recognized as especially dangerous, while the rachitic pelvis, with it!-! wide divergency from inlet to outlet, rarely causes difficulty after the inlet has been passed. During the course of study of the outcome of labor in patients in whom x-ray pelvimetry has been obtained, it was noted that pelvic shape definitely influenced the ability of the patient to deliver vaginally through the midplane. It is thought worth while to communicate this experience. :Material and Definitions
This study comprises 1,169 patients in whom x-ray pelvimetry was obtained during the period July 1, 1947, to July 1, 1950. Most of the x-rays were ohtained on patients with clinically suspect pelve~:>. Some x-rays were taken electively. These x-rays were read by both the x-ray department and the author. All pelves were classified by both the Department of Roentgenology and the author. The interspinous diameter ( I.S.) is defined as the shortest distance between the tips of the ischial spines. The anteroposterior diameter of the midplane (A.P.M.) is the distance between the lower portion of the symphysis pubis that is closest to the spines and the junction of the fourth and fifth sacral segments. The posterior sagittal of the midplane (P.S.M.) is defined as the distance hetween the I. S. diameter and the junction of the fourth and fifth sacral segments. Not all patients are included. All who had elective cesarean sections were deleted as well as patients having cesarean section for uterine inertia or inlet obstruction. Easy vaginal deliveries are those in which the patients delivered spontaneously or with forceps that did not require excessive traction. Difficult deliveries are those in which there was difficulty with rotations, when excessive traction was used, or when the baby showed evidence of intracranial injury or was stillborn because of the pelvis. Sections for midplane obstruction after trial of the midplane with labor are in the difficult group. Stillbirths from separation of the placenta, etc., were considered easy deliveries. Classification by X-ray
Table I shows how pelves are classified at various clinics throughout the United States and Great Britain. There is a moderate variation in interpreta116
Volume 63 :'\lumber I
RELATION OF PELVIC SHAPE TO MIDPLANE PROGNOSIS
117
tion. This may be due to differences in racial and economic factors. There is a moderate agreement with respect to gynecoid pelves, but the classification of other types varies considerably. I
TABLE
Sloane Hospital for Women1 Pettit, Garland, I>unn, Shumaker1 Javert, Steele, and Powlitis2 Walsh, John G.s Kenny, Meave4 Diekinson and Prooters
50.6
22.7
4.4
22.4
1.8
51.0
18.0
5.0
21.0
5.0
50.0
13.0
9.0
28.0
56.0 54.46 74.0
17.25 10.01 1.66
3.0 2.81 1.66
23.75 31.76 1.33
9.38 20.66
CLAS§IFICATIQa QF ~:l!!l;i- ElmBE liBI:lll! BASIC FORMS
448
39.0'4
118
Fig. 1.
This discrepancy was marked in our own clinic. Table II shows the lack of agreement in the same pelves between the Department of Roentgenology and the author. We agreed on both the anterior and posterior segments of the pelves in 44 per cent of the patients. We disagreed entirely in 23 per cent of the cases. We agreed on the posterior segment 57 per cent of the time and on the anterior segment 62 per eent of the time.
11 8
-----
---
J.
Ob:- 1. iX
(":;ynt'l
J .l nu :ll') ·. J <) C2
II.
CLM>8IHCATIO:" Ol' PEJ.Vb:; . Cow, ELA 'l'IO!\ (J!' INTEIU'H ET A'l'ION In: X -RAY :DEPAI:'l'MEK'r ANn Am'HOf:, .I ,149 P~; r , vEs ---------·---·- _______ __ .._______ -- - ----- ·-------
'l'ABLE -
:\ m .
KALTRBIDEl~
-- --- ---~ ---- --- ----------- -- ---- ----
·-·--
X-ray JJt:partm eut and At!tltor .dgret: on Classification oj' P dve.,
1. 2. 3. 4.
W{th botilaii teriOr- and posierior -~egmen ;:~------· --· .. - 'ii % -fi7 % With posterior segment of pelvi~ onl y ti:.! % With anterior segment of pelvis only No agreement ~~-~ith~_se~ent _ .. ___________ _____ _ :?~- ~ -- --- --· __
Fig. 1 shows how the author classified 1,149 pelves, according to their basic form, i.e., the posterior segment. Fig. 2 illustrates the classification of both segments. The total column represents the posterior segment, and the various divisions of the column represent the anterior segment. Note that this grouping does not agree to any extent with the various classifications found in Table I. At best the classification is based on visual impression and all of us obviously do not ''see'' alike. CLASSIFICATION OF PELVES- ENTIRE GROUP BASIC FORMS
448
39.0'X.
362
t9.2'X.
221
0-4-- -
Fig. 2. TABLE
III.
EASY RACE AND ECONOMIC STATUS
Negro White ward Private All ca.ses
I
ANDROID GYNECOID
%
70.2 80.0 79.6 74.7
F ACTOHS
RACIAL AND ECONOMIC
%
81.7 85.0 85.5 83.5
I
PLATY· PELLOID
%
83.4 80.0 84.6 83.3
JN DIFFICULTY OF DELIVERY DU'FICULT
I
ANTHROPOID
AKDROID
IGYNECOID
PLATYPELLOID
79.6 81.3 87.1 82.6
29.8 20.0 20.4 25.3
18.3 15.0 14.5 16.5
16.6 20.0 15.4 16.7
%
%
%
%
I ANTHROPOID %
20.4 18.7 12.9 17.4
Volume 63 Number I
RELATION OF PELVIC SHAPE TO MIDPLANE PROGNOSIS
119
Table III demonstrates the outcome of labor with respect to ease or difficulty in this series, according to pelvic shape and racial and economic factors. The android pelvis gave the most difficulty, while the remainder of the pelves had essentially the same outcome. This ease or difficulty refers to the pelvis as a whole and not to any one particular plane. CORRELATION OF I .S. AND A.P.M. DIAMETERS IN ALL PELVES 860 CASES ABOVE 9.00 M.
306 CASES
488 CASES
34 DIFFICULT
22 DIFFICULT
ILO% DIFFICULTY
4.5 'l:. DIFFICULTY
28 CASES
38 CASES
10 DIFFICULT
13 DIFFICULT
36 "4 DIFFICULTY
34% DIFFICULn
:t.s. 9.ooM. BELO w 9.0C M.
BELOW 12.0 CM
12.0 CM.
ABOVE 12.0CM.
A.P..M.
Fig. 3.
CORRELATION OF LS. AND P.S.M DIAMETERS IN All PELVES 860 CASES
ABOllE
389 CASES
406 CASES
37 DIFFICULT
18 DIFFICULT
9.5% DIFF ICULTV
4.5% DIFFICULTY
40 CASES
25 CASES
14 DIFFICULT
9 DIFFICULT
35 "/• Dl FF I CULTY
36% DIFFICULTY
9.0CM.
I.S. 9.0 CM.
BELOW 9.00M
BELOW 4.6 CM.
4.6CM. P.S.M.
ABOVE 4.6 CM.
Fig. 4.
The Midplane The transverse diameter of the midplane (I.S.) was correlated separately with the two A.P. diameters (A.P.lVL and the P.S.M.). This correlation was done by the use of seattergrams (Figs. 3 and 4). In order to find out what lengths of diameters may be considered borderline diameters, the scattergrams were divided arbitrarily into four quadrants. The percentage of difficult labors through the midplane was then calculated. These quadrants were varied in size by changing the lengths of the diameters at 0.2 em. levels. For example, in Fig. 3 the horizontal line was drawn at 9.4 em., and the vertical line was drawn at
KALTREIDER
120
Am.
J. Qb,t.
& Gynec. January, !952
11.4 em. The percentage of difficulty was then established in each quadrant. Both lines were then varied until there was the greatest difference in perrentage of difficulty in the large pelves (right upper quadrant) and the smallest pelves (left lower quadrant). In both graphs the I.S. of 9.0 em. was found to lw borderline, while the borderline A.P.M. was 12.0 ern. and P.S.l\I. 4.6 em. Jt was disturbing to note that in the large pelves (right upper quadrants of both figures) there was still difficulty of 4.5 per cent or 1 in 22. It was also noted that the length of the A.P. diameter was a factor when the I.S. diameter was CORRELATION OF I.S. AND A.P.M. DIAMETERS IN GYNECOID AND PLATYPELLOID PELVES 259 CASES 108 CASES
146 CASES
12 DIFF I CUI.. T
2 DIFFICULT
II t, DIFFICUI,. TY
1.4'4 DIFFICULTY
3 CASES
2 CASES
3 DIFFICULT
2 DIFFICULT
lOOt, DIFFICULTY
100'4 DIFFICULTY
ABOVE
9.0CM.
:r.s. 9.0 eM.
BELOW
9.0CM.
BELOW 12.0CM.
12.0CM.
ABOVE 12.0 CM.
A,P. M.
Fig. 5.
CORRELATION OF I.S. AND P.S.M. DIAMETERS IN GYNECOID AND PLATYPELLOID PELVES 256 CASES 121
128 CASES
CASES
ABOVE
9.0CM
II DIFFICULT
2 DIFFICULT
9'1:. DIFFICULTY
1.6'4 DIFFICULTY
6 CASES
I CASE
5 DIFFICULT
I DIFFICULT
83,. DIFFICULTY
100,. DIFFICULTY
I.S. 9.0CM.
BELOW
9.0CM.
BELOW 4.6CM.
4.6 CM. P.S.M.
ABOVE '1.6 CM.
Fig. 6.
of the longer variety. The difficulty was doubled when the A.P.M. was under 12.0 em. or the P.S.M. under 4.6 em. This did not hold true when the I.S. was 9.0 em. or below. Then the A.P. diameters did not appear to affect the outcome of labor. There was routinely 35 per cent difficulty when the I.S. diameter was 9.0 em. or below. Pelvic shape was considered next. Since the android pelvis is usually incriminated in midplane and outlet difficulty this group was removed 1 leaving
Volume 63 Number 1
RELATION OF PELVIC SHAPE TO MIDPLANE PROGNOSIS
121
the gynecoid, platypelloid, and anthropoid, both pure and mixed forms. There Wa.-3 no change in the amount of difficulty in the four quadrants of the scattergrams. The anthropoids were deleted next. No change noted. Finally any pelvis in which there were android or anthropoid characteristics, whether in the posterior segment or anterior segment, were deleted. Now there appeared to be a marked change (Figs. 5 and 6). Now the amount of difficulty in the larger pelves (right upper quadrant) was cut to one-third from 4.5 per cent to 1.5 per cent. There was no change in the relationship of pelves with longer LS. diameters and shorter A.P. diameters (left upper quadrant). There were very few pelves left with I.S. diameters of 9.0 em. or less, but this group was essentially 100 per cent difficult.
Comment Lilienfeld, Treptow, and Dixon6 have demonstrated that classifying pelves is not a simple procedure. Two different observers agreed on the classification of the anterior segment 52 per cent of the time and on the posterior segment 59 per cent of the time. There is apparently no uniformity in evaluation of shape by different observers. Even more important Lilienfeld and co-workers have shown that when one individual classifies a pelvis more than once he will not agree with himself more than 62 per cent of the time. For the above rea.<3ons the author is not sure that pelvic shape enters "into the picture" when evaluating the midplane. From my own interpretation of pelvic shape as seen in the x-ray it seems to be of definite help. Android and anthropoid characteristics in the midplane increase difficulty in larger pelves by 3 times, while gynecoid and platypelloid pelves with short I.S. diameters are dangerous. What the results would be, if another observer repeated this work, would be highly conjectural. It would seem worth while for it to be repeated. Conclusions 1. The classification of pelves by visual methods into gynecoid, anthropoid, platypelloid, and android is difficult. Consistency is lacking. 2. An I.S. of 9.0 em., A.P.M. of 12.0 em., and P.S.1VI. of 4.6 em. may he borderline in the midplane. 3. Patients with pelves of any shape may have difficulty in the midplane regardless of size; 4.5 per cent when the diameters are above border line; about 10 per cent when the I.S. is over border line and the A.P.M. or P.S.M. is below border line; and 35 per cent when the I.S. diameter is 9.0 em. or below. 4. Patients with gynecoid and platypelloid pelves and I.S. over 9.0 em., A.P.M. over 12.0 em. and P.S.M. over 4.6 em. will probably have little trouble. 5. An I.S. diameter of 9.0 em. or less may be more dangerous in the gynecoid and platypelloid pelves than in android and anthropoid pelves .
•
The author wishes to express his appreciation to the members of the Department of Roentgenology of the University of Maryland School of Medicine for their faithful and generous assistance in this study.
References 1. 2. 3. 4. 5. 6,
Caldwell, W. E., Moloy, H. C., and Swenson, P. C.: Am. J. Roentgenol. 41: 505, 1939. Javert, C. T- Steele, K. B., and Powlitis, M. E.: AM. J. 0BST. & GYNEC. 45: 216, 1943. Walsh, J. G.: AM:. J. OBsT. & GYNEC. 39: 255, 1940. Kenny, M.: J. Obst. & Gynaec. Brit. Emp. 51: 277, 1944. Dickinson, K., and Procter, I. M.: AM:. J. OBST. & GYNEC. 44: 585, 1942. Lilienfeld, A. M., Treptow, E., and Dixon. D. M.: Human Bioi. 21: 143, 1949,