FOR some time the x-ray has been used to advantage in diagnosis of multiple pregnancy, position of fetus and fetal abnormalities. However, it has been only the past four or five years that any definite information has been obtained by roentgenographic methods of diagnoses in pelvimetry.
At the present time we are convinced that only by means of roentgenographs can be true proportions of the superior strait be determined, and that the ordinary external methods of Pelvimetry are not only occasionally misleading but proportionately inaccurate.
The present communication deals with the method of Herbert Thomas of Yale University. This method was developed in cooperation with the late Dr. W.A. Lafield, who was Professor of Roentgenology at the Yale Medical School.
Some of the reasons why roentgen pelvimetry has not been more universally adopted are probably due to the following factors.
(1) The majority of women will be delivered normally, whether or not pelvic measurements are made.
(2) The medical profession does not readily accept a new method after an established satisfactory routine has been in use.
(3) A new method of diagnosis incurs added expense.
(4) The present methods, although entirely speculative, are satisfactory in most cases.
(5) Roentgen pelvimetry cannot be performed by the obstetrician himself but requires the aid of a roentgenologist.
(6) The value of roentgenometric diagnosis is recent in origin and as yet not universally accepted.
If the knowledge of the size and shape of the pelvis is necessary to the practice of obstetrics, roentgen pelvimetry is a sound procedure, particularly in pre-emptors patients, and should and should be considered as an indispensable aid in these cases.
The method of Herbert Thoms as developed at Yale Medical School is not the only method. However, it can be classified as simple, accurate and rapid; being adaptable for use by other than experts in x-ray and obstetric diagnosis. As a technical procedure a well trained hospital technician can master its technic alter sufficient instruction.
Studies of recent years reveal the fact that external Pelvimetry fails to give uniform and accurate information in regard to the shape and size of the superior strait. This is often true of thin undersized individuals. In many patients of this type external measurements may suggest a contracted pelvis while the x-ray will show a relatively large pelvis with a subsequent natural labor and normal-sized child. On the other hand a stocky short person with similar external measurements will disclose a contracted pelvis which is an obstetric problem. Because of the apparent relationship between shortening of the transverse diameter and a secondary persistent occipito-posterior presentation, accurate information regarding this diameter is of clinical significance.
The observations of Thomas were made on twenty consecutive patients whose pelvis showed a relative or real shortening of the transverse diameter of the superior strait. In every instance a primary or secondary occipito posterior position was found after the patient was in labor. (Herbert Thoms, Surgery, Gynecology and Obstetrics, January, 1933). It therefore has been proved that an actual or relative shortening of a transverse diameter of the superior strait results in a limitation of space that is greater in the anterior than in the posterior half of the superior strait. Under these circumstances, when the head descends early in labor, the occiput is forced to rotate posteriorly.
The x-ray offers additional information in determining the size of the fetal head. It has been noted in x-ray examination of the unengaged fetal head that it lay with the transverse diameter of the superior strait, the occiput being either to the right or left; therefore, if roentgenogram of the patient is taken in the supine position with the fetus in the uterus, it will cast a shadow which is an enlarged profile of the head. The measurements of the occipital frontal diameter of the head can then be made. On numerous occasions this method of cephalometry, determining the diameter of the unmoulded head before and after cesarean section, has yielded accurate results. (Thomas, A.M.A., February 24, 1934).
As experience increases in roentgen pelvimetry, the so-called labor test will be employed less. This, however, does not mean that the physician should not under estimate the importance of uterine contraction and the ability of the fetal head to mold. It has always followed that when something could be proved desirable in medicine for the better protection of the patient, such an advance would be demanded and eventually become routine. We may concede, therefore, that roentgen pelvimetry has a distinct place in the examination of every primiparous woman. In many instances, according to Thomas and others, external; measurements were normal but the x-ray examination revealed a contracted pelvis. On the other had, in certain patients whose external measurements suggested a cesarean section roentgen pelvimetry proved otherwise and they were subsequently delivered in a normal manner.
CENTIMETER GRID METHOD.
The procedure in this method may be summarized by stating the following:.
(1) The patient is placed on the roentgenographic table in the semi- recumbent position.
(2) The level of the superior strait above the sensitized film is established.
(3) The tube target is centered about five centimeters posterior to the symphysis, at thirty-two inches from the sensitized film, The exposure is made.
(4) The patient is removed from the table, the tube target and sensitized film remaining in situ.
(5) A lead plate, or centimeter grid, with perforations exactly one centimeter apart, is introduced into the same plane as that previously occupied by the superior strait and a second (flash) exposure is made on the same sensitized film as was used used in the previous exposure.
(6) Development of the film shows the outline of the superior strait and the shadows of the perforations, the assistance between which represents centimeters in the plane of the superior strait. The anteroposterior and transverse diameters of the superior strait in its use proportions may be drawn on centimeter-square paper by following the course of the shadow of the superior strait and transcribing it.
As this time I wish to express my thanks to Dr. Thoms for his personal advice and instruction which helped me to master the technic of his method.