MECHANISM OF LABOUR.ppt

MECHANISM OF LABOUR
By: Akadango

LEARNING OUTCOMES
 To equip students in midwifery to gain knowledge
and skill on the mechanism of labor to apply when
managing mothers during labor and delivery

SPECIFIC OBJECTIVES:
1. Explain the concept of normal mechanisms of
labor
2. Explain the normal mechanisms of labor in an
occiput anterior position
3. Identify processes in the mechanism that are
applicable in mechanisms of other head or
cephalic presentations
4. Explain factors that influence descent, flexion,
rotation and expulsion of the fetus
5. Explain the significance for the midwife of
understanding the mechanisms of labor.
6. Reflect on the consequences of not
understanding mechanisms of labor

MATERNAL –FETAL RELATIONSHIPS
Review Maternal Fetal Relationships
This is important in explaining the processes and
factors that determine how the fetus negotiates the
maternal pelvis and birth canal in labor and at birth.

Normal Relationships prior to
birth
1. Lie
2. Attitude
3. Presentation
4. Denominator
5. Position
6. Presenting part

1.Lie:
• Long axis of fetus to long axis of the
uterus:
• when the long axis of the fetus lies
parallel to the long axis of maternal
uterus this is a longitudinal relationship
as is desirable for normal mechanisms
of labor

2. Attitude:
Fetal limbs and head to its trunk:
When the fetal head is flexed with
chin on chest, back is bent, arms
flexed on the chest, thighs on
abdomen and legs on thighs then
this is an attitude of flexion

3. Presentation:
The part of the fetus that lies at the
pelvic brim or lower pole of the uterus.
Cephalic presentation refers to all head
presentations. In a well flexed head the
presentation is vertex

4. Denominator:
The part of the presentation that
determines the position of the fetus. In
vertex presentation, the denominator is
the occiput.

5. Position:
The relationship of the denominator to the six
areas of the pelvic brim (right and left
posterior, lateral and anterior. If the occiput
points to left anterior the position is left
occiput anterior.

6. Presenting part:
The part that lies over the cervical os during
labor on which the caput forms. In left occipito
anterior position, the presenting part is the
posterior part of the right parietal bone.

DEFINITION OF MECHANISM OF
LABOUR
 Cardinal movements in first and second stage of
labor
 A series of passive movements of the fetus in its
passage through the birth canal to the exterior
 The canal has different shapes with inlet and outlet
differing in size and shape
 The fetus accommodates itself to the diameters and
curve of the pelvic canal
 The knowledge is significant for the student midwife
to manage the progress of normal and abnormal
labour

MECHANISMS OF LABOR
The fetal movements occurring during
labor because of:
 expulsive uterine action
 abdominal muscle contractions,
 Diaphragm
 resistance of the pelvic floor.

MECHANISMS OF LABOR
LEFT OCCIPITO ANTERIOR POSITION
Fetal Head lies with the occiput in the
anterior part of the pelvis on the
mother’s left side
• Occiput points to the left ileo-pectineal
eminence on the left anterior area of
the pelvic brim
• Sagittal suture is in right oblique
diameter of the brim

MECHANISM OF VERTEX
PRESENTATION
The expulsive action of the uterine that
stimulates the dilatation and
effacement of the cervix moves the
fetus towards the cervix
Resistance is offered by pelvis, cervix
and pelvic floor muscles
The presenting part reaches the pelvic
bones and makes adjustments to pass
through the pelvis and down the birth
canal

MECHANISMS OF LABOR
Mechanisms of Labor
1. Engagement of the head
2. Flexion of the head
3. Descent (a continuous process)
4. Internal rotation of the head
5. Crowning of the head
6. Extension of the head
7. Restitution of the head
8. Internal rotation of shoulders
9. External rotation of head
10. Lateral flexion of the body

MECHANISMS OF LABOR
LEFT OCCIPITO ANTERIOR POSITION
The lie is longitudinal
The attitude is that of flexion
The Presentation is cephalic
The denominator is the occiput
Position is Left Occipito anterior
The presenting part is the posterior aspect of the
right parietal bone
The sub-occipito frontal diameter (SOF) (10cms) lies
at the pelvic brim. The head is usually flexed with
SOF (10cms) lying at the brim.

CARDINAL MOVEMENTS:
1.ENGAGEMENT OF THE FETAL HEAD
This is called lightening or dropping of
the fetal head into the pelvic brim
Engagement in prims may occur
during the latter weeks of pregnancy
In multigravida the muscle tone is lax
descent and engagement may not
occur until labor begins
Uterine contractions and retraction
allow progress to speed up

CARDINAL MOVEMENTS:
2.DESCENT:
 In primgravid it begins two weeks before the onset
of labor when engagement occurs unless there is
disproportion of the head
 Further descent happens in 1ST stage of labor due
to effective uterine contractions
 Meeting resistance to the cervix increases flexion of
the head
 Dilating cervix allows the fetal head to descend

CARDINAL MOVEMENTS:
3. FLEXION OF THE HEAD:
 Flexion is a function of baby’s attitude, anterior
position, and anterior position of the head and
contractions.
 When flexion is increased the Suboccipital-
bregmatic diameter(9.5cm) engages
 Smaller presenting diameter facilitates descent
 The attitude of the fetus is of flexion hence the
uterine contractions increase the existing attitude
 The occiput becomes the leading part that
influences next movement that of internal rotation

CARDINAL MOVEMENTS:
4.INTERNAL ROTATION OF THE HEAD:
 With further descent the fetal head rotates
anteriorly and the fetus assumes an oblique
position
 The fetus may rotate to occipital anterior position
• The movement causes the larger diameters of the
head,shoulders and buttocks to emerge under the
pubic arch in the antero posterior which is the
largest diameter
• The head escapes under the pubic arch and allow
the sub-occipito region to pivot on the lower border
of the symphysis pubis.

CARDINAL MOVEMENTS:
 In LOA the occiput rotates forwards 1/8 of the circle
from left ilio-pectineal eminence to the symphysis
pubis to escape under the pubic arch
FACTORS FACILITATING IR:
 Resistance of the pelvic floor muscle
 Uterine contractions causes the occiput to stretch
the left half of the pelvic floor
 The pelvic floor direct the leading part towards the
front to pass under the pubic arch

INTERNAL ROTATION OF THE HEAD:

CARDINAL MOVEMENTS:
5.CROWNING:
 It is the term used when the occipital prominence
escapes under the symphysis pubis
 A smaller diameter the SOB- 9.5cm distends the
vulval orifice instead of the larger SO- Frontal
diameter 10cm
 Head no longer receded between contractions. This
means that the widest transverse diameter of the
fetal head is born.

CARDINAL MOVEMENTS:
6. EXTENTION OF THE FETAL HEAD:
 Begins after the head crowns
 The flexion of the head is undone
 The sinciput,face and chin pass over the thinned
perineum
 It happens due to uterine and abdominal muscles
exerting downward pressure
 The SO- Frontal diameter 10cm sweeps the
perineum
 Brow,face and chin pass over the sacrum and
coccyx are over the perineum

CARDINAL MOVEMENTS:
7.RESTITUTION:
 This is turning of the head to undo the twist in the
neck that took place during internal rotation of the
head
 LOA the occiput restitutes 1/8 of the circle to the
left back to where it started before IR took place
 It helps midwife to deliver the shoulders on the right
direction to prevent laceration. LOA or ROA

CARDINAL MOVEMENTS:
8.INTERNAL ROTATION OF THE SHOULDERS:
 The shoulders in an LOA are in the left oblique
diameter of the pelvic cavity
 The anterior shoulder reaches the right side of the
pelvic floor and rotates forward bringing the
shoulders into the Antero-Posterior Diameter of the
outlet with effective uterine contractions

CARDINAL MOVEMENTS:
9. EXTERNAL ROTATION OF THE HEAD:
 Turning of the head that accompanies internal
rotation of the shoulders
 The occiput turns a further 1/8 of the circle in the
same direction as in restitution
 This indicates that the head is in antero –posterior
diameter of the pelvic outlet in readiness for
expulsion
 Allow the ER of head before the shoulders are born

EXTERNAL ROTATION OF THE HEAD:

CARDINAL MOVEMENTS:
10. LATERAL FLEXION OF THE BODY:
 Lateral flexion is a sideways bending of the spine,
which takes place while the body is being expelled
so that it conforms to the curve of the birth canal
 Anterior shoulder escapes under the symphysis
pubis
 Posterior shoulder passes over the perineum
allowing smaller diameter to distend the vaginal
orifice than if both shoulders were expelled
simultaneously
 The baby is carried forward over symphysis pubis
towards the mother’s abdomen by the midwife to
facilitate lateral flexion

MECHANISM OF LABOUR.ppt

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MECHANISM OF LABOUR.ppt