2. What constitutes pelvic narrowing, and how are we to determine that such a condition exists, as well as the variety and degree of the deformity?.
One of the most important advance in the teaching of practical midwifery is in the direction of systematic examination of the pelvis of pregnant women by means of the pelvimeter, the tape, and, most important of all, by the hand of the examiner within the pelvic cavity.
Every physician who does much obstetrical work should familiarize himself, in the first place, with the shape of the normal pelvis by examining the pelvic cavity carefully with regard to its sacral curve, depth of the lateral walls and of the symphysis pubis, the inclination of the pelvis and the degree of projection of the sacral promontory.
External measurements are not of great value, because we cannot estimate exactly the thickness of the intervening bones or of the soft parts. Still, conclusions can be formed which will enable one to determine approximately the development of the innominate bones, and the width of the transverse diameter of the pelvic, inlet. The same remarks applies with equal propriety to the external measurements of the conjugate at the brim, which is taken from the spinous process of the last lumbar vertebra, to the upper border of the symphysis, and should measure not less than 17.5 cm. )or seven inches) in the living subject.
The internal method with the left hand in the vagina, is the method which gives most accurate information, and the greater the contraction the more reliable is the result. This method is practiced as follows: With the fore- and middle fingers of the left hand in the vagina the promontory of the sacrum is touched. The keeping the middle finger on the promontory, press the side of the forefinger against the lower edge of the symphysis. The forefinger-nail of the right hand is then placed where the examining hand is touching the symphysis.
Remove the two hands together without separating them, so that the finger-nail may accurately mark where the hand was in contact with the symphysis. An assistant then with a tape measure or rule, measures then distance between the tip of the middle finger and the place where the side of the hand touched the lower edge of the symphysis. The distance is the diagonal conjugate and it usually measures half an inch more than the true conjugate which, as is well known, is four inches.
Now, one would naturally suppose that a contraction of the conjugate below four inches must exist to constitute pelvic deformity. As a matter of fact, however, the conjugate may measure four inches, and if the other diameters are reduced so that the inlet is nearly round, as in the generally small pelvic (the justo-minor type), an obstacle to the progress of labor may be encountered at the superior strait.
On the other hand, lessening of the conjugate at the brim to three and three-quarter inches or even to three and one-half inches (Winckel) as in the simple flat pelvis (the other diameters being normal) no obstacle to deliver will occur, and the deformity may remain unsuspected, although the mechanism of labor is generally altered. it is only in unfavorable complications such as would occur with a large foetus or an abnormal presentation, that serious disturbance of labor is observed.
In consequence of these peculiarities, some authors, and especially those who obtain the lowest percentages, recognize as abnormal only those cases in which arrest occurred in pelvis where contractions were three and one-half inches or less. While those who find deformity most frequent admit to their tables only those pelvis whose conjugates are diminished by only one- fifth of an inch. For practical purposes we may say that dangerous contractions exist in the generally small pelvis, though the conjugate measures full four inches, and in the flattened pelvis with ample transverse space when the conjugate is reduced to three and one-half inches.
The difficulties met with in the delivery of a child through a conjugate of four inches in the symmetrically small pelvis may be explained by the fact that the transverse diameter in a pelvis of this variety, is no longer, and may not be so long as the antero-posterior; hence diminution of the oblique diameter and greater difficulty in effecting an entrance of the head than would be the case with even a shorter conjugate and more transverse space.
Besides in these cases the obstruction to labor is not limited to the superior strait, but continues through the whole pelvis. The mechanism is that of early and complete flexion, with occasionally a delay in rotation from decreased inclination of the inferior pelvic planes-and the increase in the length of the pelvic axis.
These remarks apply with almost equal force to the generally contracted flat pelvis as regards the obstacle to labor at the superior strait, since internal palpation shows the transverse space at the brim to be diminished almost as much as the conjugate. A generally contracted flat pelvis with an antero- posterior diameter of four inches, is therefore capable of giving rise to as much difficulty as the symmetrically small pelvis of the same conjugate diameter. Normal labor is possible in either of these varieties of pelvis, though usually assistance by means of forceps is required.
The characteristics of the simple flat pelvis is the shortened conjugate diameter, extreme contraction being uncommon, the length of the conjugate rarely falling below three inches. This diameter may not fall below three and three- quarter inches, and when diminished to this slight degree only, labor many terminate without instrumental assistance, though version and forceps are alternative operations which often come into competition with each other.
3. The duty of the obstetrician when confronted by a contracted pelvis is to form as accurate on idea as possible of the type and measurements of deformity he has to deal with, and at the same time determine approximately the size, shape, and consistence of the infantile head. If the gestation has advanced to full term, we know what the average measurements of the foetal head are at this time. But it is a matter of great importance to know in the particular case in hand what the relation of the head is to the pelvis through which it must pass.
Tables have been complied which give the approximate weight of the child at different periods from the thirty-second to the fortieth week, with the appropriate biparietal diameter of the foetal head at the corresponding periods, as well as the diminished conjugate diameters to which the foetus may be expected to adapt itself at these times.
But for practical purposes such tables are useless. No one would ever be able to recall at the critical moment the information he desired, and if he could recall it the chances are that the knowledge would not be useful in solving the problem. We may determine the relative measurements of the pelvic canal at tits constricted portion, which is usually the conjugate of the superior strait, by a very simple procedure. This manoeuvre may be resorted to during gestation, or when labor has begun at full term.
To secure this information, map out by external palpation through the abdominal walls, the body of the child as accurately as possible. In the hypogastric region we search for the neck of the child, which is determined by the depression between the dorsal surface of the trunk and the region of the occiput. Then the head of the child is mapped out by bimanual examination, and to prove he corrections of the diagnosis, the head is made to descent slightly upon the examining finger within. If an assistance of intelligence is at hand, the external manipulation may be conducted by him. The head of the child is then made to descend by simultaneous pressure upon the breech and occiput.
The hand within the vagina then ascertains whether the head really descends, whether it passes the promontory, or whether rotation occurs. Where series obstacles are present it is easy to prove that the head remains with the greatest diameter above the pelvic brim, and even bulges out the region above the symphysis. Such a determination of the relation of the head of the pelvis is of decided importance in setting the time for the induction of premature labor, in serious cases of pelvic deformity, especially when we are in doubt as to the period of pregnancy. Labor can be brought on when the head can be pressed into the pelvis no further than the vertex, and delivery will be accomplished to soon if the head is pressed into the pelvis down to, or slightly below the parietal protuberances.
In case of an obstacle to labor at the superior strait, the gestation having advanced to full term, this method of determining the adaptability of the foetal head to the pelvic inlet may be of great service and enable one to choose between two or more competitive procedures. No great force is necessary to secure adaptation, and it need not be continued more than moment or two. The lower uterine segment offers no obstacle to the descent of the head. The only difficulty to be anticipated would occur in case of a woman with fat abdominal walls or with great hyperaesthesia of the uterus. Anaesthesia might be necessary. This method can never supersede internal measurements by palpation, but may be employed in conjunction with them and it has the additional merit of affording a very accurate idea of the relation of the foetal head to the pelvic inlet.
