A System of Midwifery

by Edward Rigby

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 passing 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 vagina 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 passing 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 labia, with which the head first enters the external passages, and the spot upon which the swelling of the integuments forms itself.” (Naegelé, 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 primiparæ 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 repetition of this screw-like motion, but by degrees the head not only passes 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 Naegelé 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 passes 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 circumstances 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 circumstance 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 circumstances, is required for this species of investigation.

The diagnosis of the sutures and fontanelles may be rendered more difficult by other circumstances: when there is a large quantity 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 circumstances; 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.

Such are the two positions in which the head presents during labour, and such is the manner in which it passes through the pelvis and external passages. Slight deviations do occasionally take place, the chief of which is, that the head in the second position does not always make the quarter of a turn as above described, but comes out with the anterior fontanelle forwards and to the left: this is by no means of common occurrence, and, as far as we have observed, increases the difficulty of labour very little.