Essential Factors of labour

Þ1Essential Factors of labour: Basis for Assessment

The passenger

·1 Fetal head

·2 Shoulders and pelvic girdle

·3 Fetal lie

·4 Presentation

·5 Attitude

·6 position

The passageway

·7 Pelvis

·8 Soft tissues

The powers

·9 Uterine contractions

·10Voluntary bearing-down efforts

·11Implications of nursing care

The placenta

Psychologic response

Þ1Techniques for Assessment

¨1 Abdominal palpation

¨2 Auscultation

¨3 Vaginal examination

¨4 Effacement of the cervix

¨5 Dilatation of the cervix

¨6 Station

¨7 Ultrasonography

Þ1Process of labour

¨1 Onset of labour

¨2 Mechanism of labour

¨3 Phases of the mechanism of labour in vertex presentation

¨4 Persistent occiput posterior or occiput transverse position

¨5 Duration of labour

¨6 First stage of labour

¨7 Second stage of labour

¨8 Third stage of labour

¨9 Fourth stage of labour

Labour (parturition, childbirth, birthing) is the process by which the fetus and placenta are expelled from the uterus and the vagina into the external environment.

The goals of the health team are the safe delivery of mother and child and the promotion of emotional fulfillment for the placenta.

Þ1Essential Factors of labour: Basis for Assessment

·1Parturition is the birth process.

·2A parturient is a woman in labour.

·3Labour is a coordinated sequence of involuntary uterine contractions that result in effacement and dilatation of the cervix and voluntray bearing-down efforts that result in delivery, the actual expulsion of the products of conception, the fetus and placenta.

·4eutocia is normal labour;

·5dystocia is abnormal labour or difficult labor.

In every labour five essential factors affect the process. These are easily remembered as the five P’s:

1. Passenger: size, presentation, and position of the passenger or fetus

2. Passageway:

أ) Configuration and diameters of the maternal pelvis

ب) Distensibility of the lower uterine segment, cervical dilatation, and introitus

3. Powers: strength, duration, and frequently of uterine contractions

4. Placenta: site of insertions of the placenta

5. Psychology: Psychologic state of the woman

The Passenger

The passage of the fetus through the birth canal is influenced by the size of the fetal head and shoulder, the dimensions of the pelvic girdle, and the fetal presentation and position.

Fetal head. Because of its size and relative rigidity, the fetal head has a major effect on the birth process.

The bony skull is made up of the larger and more compressible cranial vault and the smaller, incompressible face and base of the skull.

The external cranial vault is composed of

·1two parietal bones,

·2two temporal bones

·3the frontal bone, and

·4the occipital bone. These bones are united by membranous sutures:

·5the sagittal,

·6lambdoidal, and

·7coronal.

At the points of intersection, these sutures become enlarged to form the fontanels (“soft spots”)

The two most important fontanels are the anterior and posterior fontanels.

The anterior fontanel is found at the intersection of the sutures of the two parietal and the frontal bones. The larger of the two it is diamond shaped and closes at about 18 months of age.

The posterior fontanel is at the junction of the sutures of the two parietal bones and one occipital bone and is therefore triangular in shape. It is smaller than the anterior fontanel and closes by about the twelfth week of life.

The bones of the cranial vault are not firmly united, and slight overlapping of the bones, or molding of the shape of the head, occurs during labor. This capacity of the bones to slide over one another permits adaptation to the various diameters of the pelvis.

Molding can be extensive, but with most neonates the head assumes its normal shape within about 3 days after birth.

The fetal head can move on the neck about 45 degrees in flexion or extension and approximately 180 degrees during rotation. This movement permits smaller diameters of the fetal head to present during descent through the birth canal.

Principal measurements of the fetal skull are as follows (in centimeters):

1) Anteroposterior diameters

أ) Occipitomental (OM): 13.5

ب) Occipitofrontal (OF): 11.75

ج) Suboccipitobregmatic (SOB): 9.5

2) Transverse diameters

أ) Biparietal (Bip): 9.25

ب) Bitemporal (Bit): 8.0

The biparietal diameter is the largest of the transverse diameters. When the biparietal diameter has descended past the inlet (brim, or superior strait), the head become fixed in the pelvis, is said to be engaged, and is no longer freely movable.

Of the anteroposterior diameters, it can be seen that the attitude of flexion or extension allow diameters of different sizes to enter the pelvis.

The smallest diameter (suboccipitobregmatic) to present is with the head in complete flexion and thus able to enter easily, where as the largest diameter, with the head in hyperextension, is too large for the head to enter the average pelvis, and therefore the birth process will not progress.

Shoulders and pelvic girdle.

Because of their mobility, the position of the shoulder (the shoulder girdle) can be altered during labour, so that one shoulder may occupy a lower level than the other. This permits a small shoulder diameter to negotiate the passage. The circumference of the hips, or pelvic girdle, is usually small enough not to create problems.

Fetal lie

Lie is the relationship of the long axis (spine) of the fetus to the long axis of the mother. There are two lie:

· Longitudinal, in which the long axis of the fetus is parallel with the long axis of the mother, and

· transverse, in which the long axis of the fetus is at right angles to that of the mother.

· Longitudinal lies are either cephalic (head) or pelvic (breach) presentation, depending on the fetal structure that first enters the mother’s pelvis.

Presentation

Presentation refers to that portion of the fetus that enters the pelvis first and covers the internal os of the cervix, such as cephalic (vertex, head), breach or shoulder.

Presentation may also be more precisely described as a presenting part; for example, in cephalic presentation, the presenting part varies with the attitude of the fetus; in breach presentation either the sacrum (frank breach) or a foot (footling breach) may present.

Attitude

Attitude is the relationship of the fetal body parts to each other.

The fetus assumes a characteristic posture (attitude) in utero partly because of the mode of fetal growth and partly because of accommodation to the shape of the uterine cavity.

The shape is roughly ovoid,

· the back is markedly flexed,

· the head is flexed on the chest,

· the thighs are flexed on the abdomen,

· the knees are flexed at the knee joints, and

· the arches of the feet rest on the anterior surface of the legs; this is the attitude of “general flexion”.

· The arms are crossed over the thorax, and the umbilical cord lies between them and the legs.

In cephalic presentation the degree of flexion of the head on the chest determines the presenting part:

1. If the head is fully flexed on the chest, the occiput (vertex) presents first and the posterior fontanel is palpable on vaginal examination; this is termed an occipital, or vertex, presentation.

2. If the head is partially flexed or not flexed (moderate flexion), the anterior fontanel presents and is palpable on vaginal examination; this is termed a sinciput presentation or a military attitude.

3. If the head is markedly extended, the brow is the presenting part: this is termed a brow presentation

4. If the head is hyperextended, the chin (mentum) is the presenting part; this is termed a face or chin presentation.

In pelvic (breech) presentation

· the thighs may be flexed on the abdomen and the legs extended (frank breech presentation),

· the legs may be flexed on the thighs so that buttocks and feet present (complete breech), or

· one or both feet may extend downward (single or double footling breech).

Transverse lies are referred to as shoulder presentation. Unless the fetus rotates or is rotated to a longitudinal presentation, birth is possible only by cesarean delivery.

The most common presentations are vertex (96 %) and breech (3 %), The others are rarely encountered, but they act to slow or prevent the birth process.

Position

Position is the relationship of the fetal reference point (e.g., occiput, brow, chin or mentum, or sacrum) to one of the four quadrants of the mother’s pelvis; that is the most prominent and dependent portion of the presenting part is related to one of the four quadrants of the moth’s pelvis.

These quadrant’s formed by drawing an imaginary line from the moth’s sacral promontory to the upper edge of the symphysis, pubis and bisecting is transversely with a line from one side to the other, are termed the right posterior and anterior quadrants and the left posterior and anterior quadrants.

In vertex presentation, if the occiput (fetal reference point) is the most prominent portion of the presenting part and is located in the right anterior quadrant, the position is noted as right occiput anterior (ROA).