Part 14 (1/2)

CHAPTER III.

MECHANISM OF PARTURITION.

_Cranial presentations--first and second positions.--Face presentations--first and second positions.--Nates presentations._

If we were asked to point out the basis on which the principles of practical midwifery should be founded, we would answer, on an accurate knowledge of the manner in which the child presents, and pa.s.ses through the pelvis and soft parts during labour. In confirmation of this remark, we may observe, that almost every great improvement in midwifery practice which has taken place during the last century, has resulted from farther investigation into this difficult field of inquiry, and from the gradual addition of new facts to our knowledge respecting this interesting process.

Unless a pract.i.tioner be thoroughly acquainted with every step in the mechanism of a natural labour, how can he be expected to understand and detect with certainty any deviation from its usual course, still less make use of those means which may be required under the particular circ.u.mstances of the case; and yet, strange to say, there are few subjects which, generally speaking, have excited so little attention, and upon which such incorrect opinions have prevailed even up to the present time.

The investigation is confessedly one of considerable difficulty, and as it was more easy to calculate how the head ought to pa.s.s in this or that position through the pelvis than to ascertain how it really did pa.s.s, ingenuity has been taxed, and theories have been invented, and positions of the child without number have been described, which have never existed in nature, and which have only added to the difficulty and perplexity of the subject.

We consider that to form an accurate diagnosis in these cases, requires the highest perfection of the _tactus eruditus_, which can only be acquired by long practice and patient observation: and it is chiefly from this circ.u.mstance that we can explain why such gross errors and vague notions should have existed about a process of every day occurrence, and why, with but few exceptions, they should have been transmitted from one author to another even up to the present time. In the last century, when it was so much the fas.h.i.+on to resolve every physiological process into a mathematical problem, it was scarcely deemed necessary to spend much time in actual observation and examination; the proportions between the head and pelvis were ascertained, their angles were measured, and their curves determined, and from these data it was inferred, what must be the course which nature would follow; few attempted the slow but surer method of ascertaining by patient research the real facts connected with the process of parturition.

When the long axis of the child's body corresponds with that of the uterus, the child (provided the pa.s.sages are normal) can be born in that position: it matters little, as far as the labour is concerned, which extremity of the child presents, so long as this is the case; but where the long axis of its body does not correspond with that of the uterus, the child must evidently lie more or less across, and will present with the arm or shoulder, a position in which it cannot be born. In stating this, we wish it to be understood, that we merely refer to the full grown living foetus, and not to one which is premature, or which has been some time dead in the uterus, as these follow no rule whatever, hence the positions of the child at the commencement of labour resolve themselves into two divisions, viz. where the median line of the child's body is parallel with that of the uterus, and where it is not; the first we shall call _natural_, the second _faulty_, presentations of the child. A description of the natural presentations will form the contents of the present chapter.

The reader will almost antic.i.p.ate us when we state, that the natural presentations consist of two cla.s.ses, those where the cephalic, and those where the pelvic end of the child presents; in the first case, it will be a presentation of the cranium or of the face; in the second, of the nates, knees, or feet.[77]

_Cranial presentations._ The presentation of the cranium, (or _vertex_, as it has been improperly called,) is of by far the most frequent occurrence; thus, for instance, of 4042 children which were born in the lying-in hospital, at Heidelberg, 3834 presented with the head; of these the 3795 with the cranium, and 39 with the face: in either case, whether it be a presentation of the cranium or of the face, it will be either with the right or the left side more or less foremost; the former, from its greater frequency, has been called the first position of the cranium or face, the latter the second position.

_First cranial position._ It will be recollected we have stated, that the os uteri at the end of pregnancy is turned obliquely backwards, corresponding to the upper part of the hollow of the sacrum. If we examine during the first stage of labour, when it is just dilated sufficiently to allow the finger to pa.s.s, we shall feel the sagittal suture of the head running across it, dividing it into two unequal portions, the os uteri itself corresponding nearly to the middle of this suture. If the os uteri be sufficiently dilated to let us trace its course, we shall find that it corresponds more or less to the direction of the right oblique diameter, viz. that it runs from the right and backwards, obliquely forwards, and to the left. If we follow it with our finger in this last-mentioned direction, we come to a spot where it divides into or meets two other sutures; these are the right and left lambdoidal sutures, and beyond them is the hard convex occiput, the point where they meet being the posterior or occipital fontanelle. If we trace our finger along the suture in the other direction, viz. backwards and to the right, we shall come to a four cornered s.p.a.ce, where four sutures meet at right angles to each other; these are the sagittal, the frontal, and right and left coronal sutures; the open s.p.a.ce itself is the great or anterior fontanelle.

That part of the head which lies lowest or deepest in the pelvis, and which the finger first touches upon when introduced along the v.a.g.i.n.a, is the right parietal protuberance; and if the os uteri be sufficiently dilated, we distinguish it by its hard and conical feel. In primiparae, where the head usually is deep in the pelvis at the commencement of labour, and where the anterior and inferior segment of the uterus is closely stretched over it, the parietal protuberance may be felt through this part. Hence, then, the first position of the cranium, (or more correctly speaking, parietal bone,) is marked by the following characters: the sagittal suture crosses the os uteri, and runs parallel with the right oblique diameter of the pelvis: the vertex is therefore turned towards the upper part of the hollow of the sacrum, the posterior fontanelle forwards and to the left: the right perietal protuberance, therefore, is necessarily that part which is deepest in the pelvis; and the perpendicular diameter of the head, instead of corresponding to the axis of the pelvic brim, runs in an oblique direction upwards and forwards.

If the head at this early stage of labour be high up in the pelvis, viz.

has scarcely entered the brim, as is frequently the case in multiparae, the sagittal suture approaches in its direction to that of the transverse diameter, or to one between the transverse and oblique diameters, the posterior fontanelle corresponding to about the left acetabulum. The higher the head is in the pelvis, the nearer does its greater diameter correspond to the transverse one of the pelvis: the more oblique also is its perpendicular diameter, from which reason the right ear at this time can usually be felt without difficulty behind the pubic bones. Sometimes both fontanelles can be reached with equal ease; most frequently the posterior one is lowest, but occasionally the reverse is the case, and it is the anterior fontanelle, without, however, at all influencing the progress of the labour.

As the head advances through the brim and begins to enter the cavity of the pelvis, the sagittal suture corresponds more closely with the right oblique diameter, so that now the posterior fontanelle is turned towards the left foramen ovale, and as it approaches the outlet of the pelvis, the occiput advances still more forwards, although the head entirely quits its oblique position. At this stage of the labour, the fontanelles can usually be again reached with equal facility, and we find the anterior one corresponding to the right sacro-iliac synchondrosis, the occiput is completely behind the left descending ramus of the p.u.b.es, the right lambdoidal suture running parallel with it. Owing to this slight change in the position of the head, the occiput having advanced somewhat forwards, we no longer feel the right parietal protuberance to be lowest and in the centre of the pelvis, but the finger now touches upon the posterior and superior quarter of the right parietal bone, for this is the part of the head which first comes under the pubic arch, and first enters the external pa.s.sages.

If there be but little liquor amnii, or the membranes have been ruptured prematurely: if the head be firmly pressed against the os uteri, and we examine when it is not more than two-thirds dilated, we feel a puffy oedematous swelling upon that part of the head which corresponds to the os uteri. This will therefore be found to be situated upon the sagittal suture, nearly equidistant from the anterior and posterior fontanelles; it arises from the circulation in the scalp being obstructed by the pressure of the os uteri upon the head. If the remaining portion of the labour be rapidly completed, this will be the situation of the swelling with which the cranium is born; if, however, it follows a more gradual course, and the head pa.s.ses slowly through the os uteri into the v.a.g.i.n.a, as it thus advances deeper into the pelvis, and alters its position more or less, the swelling upon the sagittal suture disappears in part, and forms on that portion of the head which is advancing under the pubic arch, and is now tightly encircled by the external pa.s.sage: we shall, therefore, find that this second swelling is situated upon the posterior and superior quarter of the right parietal bone, and this is precisely the situation of the swelling of the head, which the child is usually born with.

From these facts we may deduce the following simple law respecting the mechanism of parturition, where the head presents: viz. that the head enters, pa.s.ses through, and emerges from, the pelvis obliquely; and this is the case not only as to its transverse diameter, but also as to the axis of its brim; the side of the head being always lowest or deepest in the pelvis. This shows the beautiful mechanism of the process, for, on account of its oblique position, there is no moment during the whole labour at which the greatest breadth (still less length) of the head is occupying any of the pelvic diameters; even at the last, when the head is pa.s.sing under the pubic arch, the complete obliquity of its position, in order that it should take up the least possible room, is very remarkable; for the ring of soft parts, by which the head is now encircled, pa.s.ses obliquely across it, running close behind the left, and before the right parietal protuberance. The head never advances with the occiput, forwards, under the pubic arch, as is stated in works on midwifery, still less with the sagittal suture parallel to the antero-posterior diameter of the pelvis; for the direction of the right lambdoidal suture, as also of the posterior fontanelle, and the position of the cranial swelling, or _caput succedaneum_, as it has been called, completely prove the inaccuracy of such a theory, the sagittal suture crosses the left labium at an acute angle, the right lambdoidal suture being parallel with the left descending ramus of the ischium.

Not less incorrect is the theory (for we can call it nothing else) of the head presenting with the vertex, and turning with its long diameter, from the oblique, into the antero-posterior or conjugate diameter, and the face into the hollow of the sacrum, for it is disproved by all the above-mentioned facts, which careful examination during labour puts us in possession of. When the head is born, the face looks backwards and to the right, viz. to the back part of the mother's right thigh, for the shoulders are by this time pa.s.sing through the pelvis in its left oblique diameter, the right shoulder being forwards and to the right, and lowest in the pelvis: it is also that which is first expelled.

Such is the manner in which the head presents in the first or most common position: a slight modification of it is occasionally observed during the early stages of labour, without influencing the favourable character of its progress: the head at first is in the left oblique diameter of the pelvis, the occiput towards the left sacro-iliac synchondrosis, the anterior fontanelle towards the right acetabulum; but as the labour advances, the head turns, so that the occiput corresponds to the left acetabulum, the anterior fontanelle being turned towards the right sacro-iliac synchondrosis, the sagittal suture running parallel with the right oblique diameter of the pelvis. This peculiar commencement of the labour is probably not detected so frequently as it really occurs, owing to its changing into the common position at so early a period.

_Second position of the cranium._ The other or second position of the cranium is, where the _left_ side of the head presents. It is, in fact, merely the reverse of the one just described: the sagittal suture crosses the os uteri at the beginning of labour, as in the former case, only now the posterior fontanelle is turned to the right instead of to the left; it is the _left_ parietal protuberance which is deepest in the pelvis, and which the finger first touches upon. As the labour advances, and the head approaches the pelvic outlet, it is the posterior and superior quarter of the _left_ parietal bone which first enters the v.a.g.i.n.a and protrudes through the os externum, and upon which the swelling of the scalp or _caput succedaneum_ is situated.

The chief peculiarity is, that the change, which we noticed in the first position as an occasional occurrence at the beginning of labour, is in this case the regular commencement of it. In the second cranial position, the head at the beginning of labour, with very few exceptions, is always with its long diameter parallel with the right oblique diameter of the pelvis, the posterior fontanelle turned towards the right sacro-iliac synchondrosis, the anterior one towards the left foramen ovale. During the early periods of labour, when the head is pa.s.sing through the brim, both fontanelles may be reached; and, generally speaking, the posterior one with greater ease, from its being usually somewhat the lower; but as labour advances, and the head has fairly engaged in the pelvic cavity, they may both be reached with equal ease, the anterior fontanelle still corresponding to the left foramen ovale, or rather to the descending ramus of the left pubic bone. ”As soon as the head experiences the resistance which the inferior part of the pelvic cavity opposes to it, or, in other words, the oblique surface which is formed by the lower end of the sacrum, the os coccygis, the ischiadic ligaments, &c. by which it is compelled to move from its position backwards in a direction forward, it turns by degrees with its greater diameter into the left oblique diameter of the pelvic cavity, viz. the posterior fontanelle is directed to the right foramen ovale, and as the head approaches nearer and nearer to the inferior aperture, it is the posterior and superior quarter of the left parietal bone which is felt in the cavity of the pelvis opposite to the pubic arch, so that when the point of the finger is introduced under and almost perpendicular to the symphysis pubis, it touches nearly the middle of the posterior and superior quarter of the left parietal bone: and this is precisely the part, as the head advances farther, which first distends the l.a.b.i.a, with which the head first enters the external pa.s.sages, and the spot upon which the swelling of the integuments forms itself.” (Naegele, _Mechanism of Parturition_, transl.)

The manner in which this change in the position of the head takes place, varies a good deal in different labours: in primiparae it usually takes place slowly, and requires several pains before it is completed; as the pain comes on, the posterior fontanelle, which was backwards and to the right, now advances more forward and comes more within reach; the anterior fontanelle, which was towards the left foramen ovale, retreats, so that when the pain has reached its maximum the head will for a moment be felt in the transverse diameter of the pelvis, and again resumes its former position as the pain goes off: with the recurrence of each pain there is a repet.i.tion of this screw-like motion, but by degrees the head not only pa.s.ses from the right oblique into the transverse diameter, but from the transverse into the left oblique, so that at length the anterior fontanelle corresponds to the left sacro-iliac synchondrosis, and the posterior one to the right foramen ovale.

In women who have already had children, the whole change is frequently effected during one pain, so that the head, which but a few minutes previously was presenting in what is called the third position of the German schools, will now be found to be in the second.

It is to the celebrated Naegele of Heidelberg that we are indebted for having first pointed out the uniform occurrence of this change in the second position. From his extensive and accurate observations, confirmed since by ourselves, as well as by many others, the head presents with the occiput _originally_ forwards and to the right very rarely, but pa.s.ses into this position during the course of labour. No one has ever described the mechanism of parturition so minutely and correctly; and the value of his investigations is the more enhanced, when we recollect what erroneous notions have prevailed upon this important subject up to the present time.

”In the former part of my practice,” says this distinguished obstetrician, ”not knowing that the head made this turn, I always concluded that my examinations in the early part of labour were incorrect, and was very uneasy that I did not find it all exactly as the books described, and attributed my want of success in ascertaining the position to my own awkwardness. At length in a private case, in which I was much interested, I again felt what I thought was the anterior fontanelle towards the left foramen ovale; and circ.u.mstances occurring which rendered it necessary to apply the forceps and terminate the labour, I found that the head had been actually in the position which I imagined I had felt. Since this time I have, in many cases, sat by the bed-side during the whole labour, with my finger upon the head, and thus come at the truth.” (_MS. Lectures._)

The very circ.u.mstance of this change in the position of the occiput from the sacro-iliac synchondrosis to the foramen ovale of the same side, is of itself quite sufficient to mislead; nor is it to be wondered at that it should have been so long unnoticed, when we recollect how difficult the examination is at this early stage of labour, and how few give themselves the trouble to attain that degree of dexterity and tact, which, even under the most favourable circ.u.mstances, is required for this species of investigation.

The diagnosis of the sutures and fontanelles may be rendered more difficult by other circ.u.mstances: when there is a large quant.i.ty of liquor amnii between the head and membranes, it renders the diagnosis exceedingly obscure in the early part of labour. In some cases the cranial bones are remarkably thin and yielding, and communicate a sensation to the finger as if it were touching a fontanelle; in others, the sutures run an irregular course, and form ossa triquetra, &c. which may easily mislead. We may also notice the changes, already mentioned, which are produced by the death of the child, and the various congenital anormalities of hydrocephalus, acephalus, &c. &c. In some cases the sagittal suture is continued backwards through the occipital bone, dividing it into two equal portions, and thus making the posterior fontanelle four cornered, and not to be distinguished from the anterior. Nor is it always easy to distinguish the posterior from the anterior fontanelle under more normal and favourable circ.u.mstances; for it would be hazardous to conclude that it is the posterior fontanelle merely because we feel three sutures meeting together, as it may possibly be the anterior one, and we are not able to reach the sagittal suture beyond. In this case we may ascertain which it is by the following rule: if it be the posterior fontanelle in the first position we shall feel a suture running more or less forwards (the right lambdoidal,) but none backwards; but if it be the anterior fontanelle forwards and to the left, we shall also feel a suture (the right coronal) running backwards. Lastly, in the second cranial position the face when born turns to the posterior surface of the mother's left thigh.