CHAPTER X
PRESENTATION AND POSITION OF THE FETUS
Returning for a moment to the pregnant uterus at term, we find it to be a thin-walled, muscular sac containing the mature fetus, attached by means of the umbilical cord to the placenta and floating in the amniotic fluid, which is contained within a sac formed by the amniotic and chorionic membranes.
The average fetus at term is about 50 centimetres long, weighs about 3250 grams and is curved and folded upon itself into an ovoid mass, occupying the smallest possible space. (Fig. 50.) Its most frequent attitude is with the back arched; the head bent forward, with chin resting upon chest; arms crossed upon chest below chin; thighs flexed upon abdomen and knees bent.
With a few exceptions the long axis of the fetus is parallel to the long axis of the mother, and most frequently the head is downward. It was formerly believed that the child stood upright in the uterus until toward the end of pregnancy and then somersaulted to the position it occupied immediately before birth. (Fig. 51.) But it is now known that though the fetus may move about and change its position during the early part of pregnancy, it is not likely greatly to alter its relation to the mother’s body during the tenth lunar month.
It seems advisable to define here certain terms which are in common use in discussing patients in labor, and which will be employed in the following pages.
A _nullipara_ (0–para) is a woman who has not had children.
A _primigravida_ is a woman who is pregnant for the first time.
A _primipara_ (1–para) applies to a woman during her first labor and until the beginning of her second labor.
_2–para_, _3–para_ and _4–para_ apply to women in succeeding labors which correspond to the numerals used.
A _multipara_ is a woman who has had more than one child.
There is also a terminology, with abbreviations, which is fairly generally used in this country and England to designate the position which the child, about to be born, occupies in relation to its mother’s body. A diagnosis of this position is, of course, absolutely necessary to a skilful management of labor, and the nurse should understand the meanings of the terms used, and also their distinctions and subdivisions.
The _presentation of the fetus_ is the term which is employed to indicate the part of the baby’s body which is at the brim of the mother’s pelvis. Thus the part of the fetus which is lowermost is designated as the _presenting part_ and gives the presentation its name. If the breech is downward, therefore, it is a _breech_ presentation (Fig. 52), and if the head is the lower pole it is termed a _head_, or _cephalic_ presentation. (Fig. 53.) The head presentations are divided into two main groups, which are designated, respectively, as _face_ and _vertex_ presentations. For example, if the baby’s neck is so arched that the chin rests upon the chest, the crown of its head, or the vertex, is the part that is lowest in the birth canal and is the part that will be seen first at the vaginal outlet. Therefore, this is called a vertex, or occipital presentation. But if the neck is bent sharply backward, the face becomes the presenting part and we have a face presentation.
The breech, face and vertex presentations are sometimes referred to as _longitudinal presentations_ since in these instances the long axes of the bodies of mother and child are parallel. In _transverse presentations_, however, the child lies across the uterus, with one side or the other at the pelvic brim.
The transverse presentations are infrequent, occurring once in about 250 cases, and are regarded as abnormal because spontaneous delivery under such circumstances is extremely rare. They are more likely to be seen, when they do occur, among multiparæ and women who have contracted pelves.
The longitudinal presentations, however, constitute something over 99 per cent. of all cases and are regarded as normal, since the child occupying this relationship may be born spontaneously. In about 3 per cent. of the longitudinal presentation the breech is the presenting part and in about 97 per cent. it is the head. Of these, the vertex presentation is the one most commonly seen and is the one in which the child is most easily delivered. Face presentations are very rare, occurring in only a fraction of 1 per cent. of all cases.
In addition to the child’s presentation, there is also its _position_, which is an entirely different matter, for in each longitudinal presentation the presenting part may occupy any one of six positions.
By _position_ is meant the relation of some arbitrarily chosen point on the presenting part of the fetus, to the right or left side of the mother, and to the front (anterior), side (transverse) or back (posterior) segment of that side.
Taking these up in turn, we find, that in transverse presentations the shoulder, _acromion_ process, is the point on the baby’s body which is chosen, to give the four possible positions their names.
In breech presentations the sacrum is the arbitrarily chosen point.
In face presentations it is the chin, or _mentum_, while in vertex presentations the occiput is the point chosen.
Presentation, then, describes the relation of the long axis of the entire fetal body to the mother’s body, while position describes the relation between the baby’s shoulder, sacrum, face or occiput to the mother’s pelvis.
If the child is so placed in the uterus that the head is the presenting part; the neck arched with chin on chest, and the occiput directed toward the mother’s left side, and more to the front than to the side, the presentation would be longitudinal, of the vertex variety, and the position would be a left-occipito-anterior. The arbitrarily chosen point on the child’s body (the occiput) would be directed toward the left, anterior segment of the mother’s pelvis. This is the situation most commonly seen and the description of this presentation and position are abbreviated, by taking the first letter of each word, into L. O. A.
If the occiput were turned directly toward the mother’s left side, neither to the front nor the back, we should have a left-occipito-transverse, L. O. T., and if it were directed toward the left posterior segment of the pelvis the position would be left-occipito-posterior, or L. O. P. As there are three corresponding positions on the right side, anterior, transverse and posterior, there are six possible positions for the child to occupy in the vertex, or occipital presentations, as follows:
Left-occipito-anterior, abbreviated to L.O.A. Left-occipito-transverse, abbreviated to L.O.T. Right-occipito-posterior, abbreviated to L.O.P. Right-occipito-anterior, abbreviated to R.O.A. Right-occipito-transverse, abbreviated to R.O.T. Right-occipito-posterior, abbreviated to R.O.P. (Fig. 54.)
Similarly there are six face (Fig. 55) and six breech (Fig. 56) presentations. Thus, if the chin (mentum) is resting in the left anterior segment of the mother’s pelvis, the position would be left-mento-anterior, or L. M. A. If the breech presents and the sacrum is in that relation the position is left-sacro-anterior, or L. S. A.
In describing the transverse presentations, four words, instead of three are used; thus, left-acromio-dorso-anterior, or L. A. D. A.
There are but four varieties of transverse presentations, since the shoulder is either anterior or posterior: thus left-acromio-dorso-anterior, left-acromio-dorso-posterior and the two corresponding positions on the right side.
During the last two to four weeks of pregnancy, particularly among the primiparæ, the top of the fundus settles to the level which it reached at about the eighth month, and the lower part of the abdomen becomes more pendulous than formerly. The patient usually breathes much more comfortably after this change in contour takes place, but, at the same time, she may have cramps in her legs as a result of the increased pressure; more difficulty in walking; frequent micturition and desire to empty her bowels, while the vaginal discharge may be considerably increased. It is at this time that the presenting part enters the superior strait and is spoken of as being “engaged.”
The time at which engagement takes place depends upon three factors: Whether the patient is a multipara or a primipara; the size and normality of the pelvis; the size and position of the fetus. It is often helpful to the obstetrician in planning for the delivery to know whether or not the presenting part is engaged, particularly in primiparæ.
Although in primiparæ engagement usually occurs about four weeks before labor begins, it does not normally take place in multiparæ until immediately before labor. This difference is accounted for in the increased tonicity of the uterine and abdominal muscles of primiparous women. In certain abnormalities, or marked disproportion between the diameters of the child’s head and mother’s pelvis, engagement may not take place until labor is well advanced, or possibly not at all.
The presentation and position of the fetus are ascertained by means of abdominal palpation, vaginal examination, rectal examination and auscultation of the fetal heart.
Palpation of the child’s body through the mother’s abdominal wall is possible under ordinary conditions, because the uterine and abdominal muscles are so stretched and thinned that the various parts may be made out through them. But it is sometimes difficult in hydramnios and is practically impossible in very fat patients or in the case of a ruptured uterus when the fetal outline is obscured by hemorrhage. This procedure has been practiced only during comparatively recent years, and is regarded by many obstetricians as one of the most important factors in reducing the frequency of puerperal infections and thus in decreasing maternal deaths. The explanation is that in general the dangers of puerperal infection are believed to increase in direct proportion to the number of times a patient is examined vaginally; and since it has been known how to diagnose the child’s position by means of abdominal palpation, the necessity for vaginal examinations is not so great and they are accordingly made less frequently.
Rectal examinations may also be regarded as a factor in preventing infection, for, since much the same information may be obtained by means of them as by vaginal examinations, after the onset of labor, they often replace direct exploration of the easily infected birth canal.
Abdominal palpation, as usually practiced, consists of four maneuvers, with the patient lying flat and squarely on her back with the abdomen exposed. The nurse should bear in mind that successful palpation requires even pressure. Cold hands applied to the abdomen or quick, jabbing motions with the fingers will usually stimulate the muscles lying beneath them to contract, thus somewhat obscuring the outline of the child. Such palpation is also very uncomfortable for the patient; but firm, even pressure, started gently, with warm hands, does not hurt.
_First Maneuver._ The purpose of the first maneuver is to ascertain what is in the fundus; this is usually either the head or the breech. The nurse should stand facing the patient and gently apply the entire tactile surface of the fingers of both hands to the upper part of the abdomen, on opposite sides and somewhat curved about the fundus. (Fig. 57.) In this way the outline of the pole of the fetus which occupies the fundus may be made out. If the head is uppermost, it will be felt as a hard, round object which is movable or _ballottable_ between the two hands, and if the breech, it will be felt as a softer, less movable, less regularly shaped body.
_Second Maneuver._ Having determined whether the head or the breech is in the fundus, the next step is to locate the child’s back and the small parts in their relation to the right and left sides of the mother. This is accomplished by slipping the hands down to a slightly lower position on the sides of the abdomen than they occupy in the first maneuver, and making firm, even pressure with the entire palmar surface of both hands. The back is felt as a smooth, hard surface under the palm and fingers of one hand, and the small parts, or hands, feet and knees, as irregular knobs or lumps, under the hand on the opposite side. (Fig. 58.)
_Third Maneuver._ Unless the presenting part is engaged, the third maneuver virtually amounts to a confirmation of the impression gained by the first maneuver, by showing which pole is directed toward the pelvis. The thumb and fingers of one hand are spread as widely apart as possible, applied to the abdomen just above the symphysis and then brought together to grasp the part of the fetus which lies between them. If not engaged, the head will be felt as hard, round and movable, while the breech will be less clearly defined. (Fig. 59.)
_Fourth Maneuver._ The fourth maneuver is of particular value after the presenting part has become engaged. The nurse faces the patient’s feet in this position, and directs the first three fingers of each hand down into the pelvis, on either side of the fetus, to ascertain whether it is a face or vertex presentation, by discovering whether chin or occiput is the higher cephalic prominence in the mother’s pelvis. (Fig. 60.) If it is a vertex presentation, the neck will be flexed, with the chin on the chest and consequently higher in the pelvis than the occiput. The nurse’s fingers of one hand will accordingly come in contact with the chin on the side opposite to the child’s back, before the fingers of the other hand reach the occiput. If, however, it is a face presentation, the neck will be bent sharply backward and the nurse’s fingers will feel the occiput first, and on the same side as the baby’s back. This maneuver tells, also, how far into the pelvis the presenting part has descended.
=Vaginal Examination.= The information obtained by vaginal examination, before the cervix is dilated, is rather uncertain since the child’s presenting part must be palpated through the fornix. But after complete, or even partial dilatation, the exploring finger is able to feel the sagittal suture and one fontanelle, in a vertex presentation, and diagnose the position by discovering the direction of the suture and whether it is the anterior or posterior fontanelle that is felt. The anterior fontanelle, it will be remembered, is relatively large and four-sided, while the posterior is small and more nearly triangular in shape. In a face presentation, the features may be felt; in a breech the examining finger can palpate the buttocks and genital crease.
Because of the possible danger of introducing infective material into the birth canal, the tendency is to make fewer and fewer vaginal examinations, and then only after the most painstaking preparation which will be described presently. Needless to state, vaginal examinations are not within the province of the nurse.
=Rectal Examinations.= More and more frequently rectal examinations are being employed to obtain information about the child’s position, as the examining finger is able to feel the surface of the presenting part through the recto-vaginal septum, after the cervix is dilated, and there is no danger of infecting the birth canal while so doing. For this reason nurses are frequently taught to make rectal examinations, thereby increasing the value of their assistance to the doctor in watching the progress of labor. (Fig. 62.)
=Auscultation of the fetal heart= is valuable in confirming the diagnosis of presentation and position which has been made by palpation. In vertex and breech presentations the heartbeat is best heard through the baby’s back and in face presentations it is transmitted through the chest, which presents a convex surface in this case and fits into the curve of the uterine wall. In anterior vertex presentations the heart is heard a little to the side and below the umbilicus; in transverse, further to the side, and in posterior, well toward the back.