1. MECHANISMS OF NORMAL LABOR
Hidayat Wijayanegara

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

3. 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

4. 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

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

6. 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

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

8. . 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

10. 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

13. 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

14. 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

15. Varieties of presentation and positionOA
ROA LOA
ROT LOT
ROP LOP OP

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

21. 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

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

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

26. 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

27. 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

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

29. 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

30. 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)

31. 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

33. 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

34. 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

37. 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

38. 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

39. 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

40. 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

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

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

47. 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

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

49. 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

51. 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

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

53. 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

56. 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

57. 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.

59. Thank You