MECHANISMS OF NORMAL LABOR Hidayat Wijayanegara

I. Lie, presentation, attitude and position Fetal orientation can be established clinically : abdominal palpation vaginal examination auscultation sonography X-Ray

Fetal lie Is the relation of the long axis of the fetus to that of mother Longitudinal - transverse - oblique Longitudinal lies are present in over 99 percent of labor at term Predisposing factors for transverse lie : multi parity placenta previa hydramnios uterine anomalies

Fetal presentation The presenting part : portion of the body of the fetus is either foremost within the birth canal or in proximity to it Can be felt through the cervix on vaginal examination Determines the presentation

In longitudinal lie  creating cephalic and breech presentation In transverse lie  the shoulder presentation

Cephalic presentation 1. The head is flexed sharply  The chin is contact with the thorax The occipital fontanel is the presenting part Vertex or occiput presentation

Cephalic presentation 2. Face presentation : Fetal neck  extended  Occiput & back come in contact The face is foremost in the birth canal Face presentation

. Vertex presentation --- Face presentation Sinciput presentation The fetal head partially flexed Anterior/large fontanel is the presenting part Brow presentation Partially extended Brow is the presenting part . Vertex Face presentation Transient presentation Labor progresses Labor progresses

Breech presentation There are three general configuration : Frank breech presentation : The thighs are flexed The legs extended over the anterior surfaces of the body Complete breech presentation : The thighs are flexed on the abdomen & the legs upon the thighs Incomplete; footling breech presentation : One or both feet/knees are lowermost

Fetal attitude or posture The head is sharply flexed The chin is almost contact with the chest The thighs are flexed over the abdomen The legs are bent at the knees The arms usually crossed over the thorax  Accomodation to the uterine cavity

Fetal position The relation of an arbitrarily chosen portion of the fetal presenting part to the right or left side of the maternal birth canal Each presentation there maybe two position, right or left The determining part of : vertex  occiput face  chin (mentum) breech  sacrum

Varieties of presentation and position OA ROA LOA ROT LOT ROP LOP OP

A. Abdominal palpation - Leopold maneuvers Diagnosis of fetal presentation and position A. Abdominal palpation - Leopold maneuvers Conducted systematically

B. Vaginal examination Three maneuvers : 1. Two fingers of either gloved hand are introduced into the vagina and carried up to the presenting part The differentiation : vertex face breech

2. If the vertex is presenting : Sagittal suture (?) Small & large fontanels 3. The station  is established

C. Auscultation D. Sonography Does not provide reliable information concerning fetal presentation & position D. Sonography Fetal head & body can be located

Labor with occiput presentation 95% of all labors  the fetus is in the occiput or vertex presentation In the majority of cases  the vertex enters the pelvis with the sagital suture in the transverse pelvic diameter Left occiput transverse (LOT) : 40% of labors Right occiput transverse (ROT) : 20% of labors Occiput posterior : 20% of labors

Cardinal movement of labor Irregular shape of the pelvic canal The relatively large dimensions of the mature fetal head A process of adaptation or accomodation of suitable portion of the head to the various segments of the pelvis is required for vaginal delivery

The cardinal movements of labor : - engagement - extension - descent - external rotation - flexion - expulsion - internal rotation

For purposes of instruction, the various movement often are described as though they occurred separately and independently  in reality the mechanism of labor consists of a combination of movements that are ongoing simultaneously For example : - as part of the process of engagement  there is both flexion and descent of the head

Engagement : The greatest transverse diameter (BPD) in occiput presentation, passes through the pelvis inlet In many primigravida this phenomena may takes place during the last weeks of pregnancy In many multiparous and some nulliparous  the fetal head is still freely movable above the pelvic inlet (floating)

Asyinclitism The sagital suture, entering the pelvic inlet may not lie exactly midway between the symphysis and sacral promontory The sagital suture deflected either posteriorly toward the promontory or anteriorly toward the symphysis Such lateral deflection of the head to a more anterior or posterior position is called asynclitism  anterior & posterior asynclitism

Descent The first requisite for birth of the infant In nulliparas, engagement may take place before the onset of labor  and further descent takes place at the second stage Four forces : a. pressure of amniotic fluid b. direct pressure of the fundus upon the breech with contraction c. bearing down effort d. extension and straightening of the fetal body

Flexion Resistance from the cervix, wall of the pelvis, pelvic floor  flexion of the head The chin more contact with the fetal thorax Suboccipito bregmatic diameter is substituted for the longer occipito frontal diameter

Internal rotation The occiput gradually moves anteriorly toward the symphysis pubis or less commonly, posteriorly toward the hollow of the sacrum Is always associated with descent Is not accomplished until the head has reached the level of the spine and thereafter is engaged

Calkins (1939) Concluded : Two thirds  internal rotation is completed by the time the head reaches the pelvic floor A fourth  internal rotation is completed very shortly after the head reaches the pelvic floor 5 percent  internal rotation does not take place

Extension Extension brings the base of the occiput into direct contact with the interior margin of the symphysis pubis Causes of extension : The vulva outlet is directed upward and forward

Two forces come into play : a. Exerted by the uterus  act more posteriorly b. Resistant pelvic floor and the symphysis acts more anteriorly  the resultant vector is in the direction of the vulva opening  causing extension

External Rotation The delivered head next undergoes restitution If the occiput was originally directed toward the left  it rotates toward the left ischial tuberosity

Expulsion After delivery of the shoulders, the rest of the left body is quickly extruded

Changes in shape of the fetal head 1. Caput Succedaneum The formation of swelling due to stagnation of fluid in the layers of the scalp beneath the girdle of contact The girdle of contact is either : Bony Dilating cervix Vulval ring

The swelling : Diffuse Boggy Not limited by the suture line Disappears spontaneously within 24 hours after birth Occurs after rupture of the membranes

Importance It signifies static position of the head for a long period of time Location of the caput  gives an idea about the position of the head occupied in the pelvis and the degree of flexion achieved : in left position  caput in right parietal bone in right position  on left parietal bone With the increasing flexion  the caput is placed more posteriorly

Moulding The alteration of the shape of the forecoming head while passing through the risistant birth passage during labor Mechanism : There is compression of the engaging diameter of the head with corresponding elongation of the diameter at right angle to it Moulding disappears within few hours after birth

Grading Grade 1 : The bones touching but not overlapping Grade 2 : Overlapping but easily separated Grade 3 : Fixed overlapping

Importance Slight molding is irritable and beneficial  the head to pass more easily through the birth canal Extreme molding (CPD)  may produce severe intracranial disturbance in the form of tearing of tentorium serebelli or subdural haemorrhage Shape of the molding  give an information about the position of the head occupied in the pelvis

Cephalhematoma A collection of blood in between the pericranium in the flat bone of the skull Unilateral Over a parietal bone Due to rupture of a small emissary vein from the skull and may be associated with fracture of the skull bone

Causes : - following normal delivery - forceps delivery The swelling is limited by the suture lines It is circumscribed, soft, fluctuant, incompressible Prognosis is good  the blood is absorbed in cause of time (6-8 weeks) leaving an entirely normal skull.

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