The first position is the commonest, and occurs in 65 out of every 100 cases; the third position comes next in 20 cases out of 100, the second position in 10, and the fourth in 5 out of 100.
The child's bead is downwards in 97 out of every 100 labours, and it is therefore un necessary to consider here the odd 3 out of every 100 in which some other part of the child presents first.
Now we have mentioned these positions for a definite reason. If one pictures to one's self the child head downwards in the womb, its buck to the mother's left side, and its face looking backwards, and to the mother's right buttock, and if one further thinks of the womb contract ing to force the child downwards through the vaginal outlet to the outside, it will be under stood what the first effect of the downward pressure will be. Suppose a child upside down, and the buttocks pressed on while something resists the advance of the head, the first thing that happens will be that the head will be bent and the chin pressed on to the chest. The back part of the head will thus be forced out of the womb first, and the head will come through, not broadside on, but lengthways, in a line from the back of the head to the chin. It will pass through more easily this way, and the child's head being still soft, and the bones not yet all united, it will be moulded gradually, and this moulding will make the child, for the time being, long-headed so to speak.
As the head progresses through the bony brim of the pelvis (see Fig. 24, p. 63) it gets down into the lower part of the pelvis, where there is more space, and as the pressure is renewed from above the head will continue to advance in the direction of least resistance.
While the child's head is at the brim of the pelvis, there is more room to pass in a diagonal direction than in a line straight from front to back, or from side to side, in the lower part of the pelvis, on the other hand, the greater room is from front to back. Thus as the head continues to advance, merely because it moves in the direction of least resistance, it tends to make a partial turn, till when it reaches the external opening the head has so turned that the face is looking directly backwards, and the neck is still strongly bent, chin towards chest. The first part to be born is, therefore, the back of the head, which comes out just below the pubic bones of the mother (see Fig. 24, p. 63). As the pressure continues from above outwards, the back of the head will bend upwards in front of the mother, and the face will sweep along the curve of the mother's pelvis behind, the face being directed straight back to the bowel of the mother, and the eyes, nose and mouth of the child will appear succes sively, directly in front of the outlet of the mother's bowel. When the chin of the child reaches the outlet, it will tend to be caught by the tightly stretched back edge of the outlet, but if at this moment the assistant places his hand on the back of the child's head, and slightly bends the head towards the child's chest, the chin will be released and will slip out.
Now at this moment, when the child's head and face are born, its shoulders will be passing through the brim of the pelvis; and if one thinks of the position of the child—upside down, its face looking directly backwards — it will be evident that its shoulders would be expected to lie right across the brim, its left shoulder to the mother's left side. But this, as already
noted, is not the line of greatest room. As the pressure continues, and the shoulders ad vance in the direction of least resistance, like the head, they will also perform a turning movement till the child's left shoulder turns into the mother's left side behind, and the child's right shoulder into the mother's right side in front. Lower down in the pelvis, where the greatest room is, as stated, from front to back, the child's leading shoulder—the right—will like the head, turn till it is directed to the front, while the left is directed to the back. The head, being born and free to move, will indicate that this movement has occurred by the child's face turning upwards towards the mother's right thigh, the mother lying on her left side. When the leading,or right, shoulderof the child reaches the front of the mother, it is caught or detained by the bony arch of the pubis of the mother's front, and meantime the child's left shoulder sweeps behind over the same ground already traversed by the child's face, and is born first, the right shoulder in front immediately follow ing, and the rest of the body quickly and easily thereafter.
There is nothing remarkable in these move ments. If one pushes a somewhat flexible rod through a narrow curved passage, the rod, meeting resistance to its passage, in obedience to the pressure from behind, will twist and turn, following the curves of the passage. So the movements of the child through the passage obey the same mechanical laws, simply follow ing the pathway of least resistance. When the energies of the mother are adequate, and no unusual obstruction or narrowing exists in the passage, the process of child-birth is largely a mechanical obedience to physical laws.
But when the energy of the mother is little and easily exhausted, the child exceptionally large, or the passage unduly narrow, difficulties arise, and help has to be rendered.
The usual form of help consists in slipping instruments, called forceps, into the passage and over the child's head, and by means of them pulling . the head down during each labour " pain," and thus helping the effort of the womb to expel the child. It will be evident, however, that if this is to be done with the greatest degree of safety to the mother and child, and with the greatest degree of ease, it must be done by someone who can determine accurately the position in which the child's head is lying, and so adjust the instruments properly, and who is also, from his knowledge, able to say in which direction the head would naturally turn in its progress outward.
While, then, labour is in the vast majority of cases attended by little difficulty, and little in terference is required, nevertheless the mother should always be attended by someone fitted, alike by knowledge, training, and experience, to recognize when assistance does become need ful, and able to render it without delay.