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Labor and Birth Processes
Chapter 18
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The 5 Ps of Labor:
Passenger (fetus)
Powers (uterine contractions)
Passage (the pelvis & maternal soft
parts)
Position (maternal)
Psyche (maternal psychological status)
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PASSENGER (FETUS):
Biological influences
A pregnancy that terminates during the 38-
42 week gestation is likely to indicate ahealthy fetus.
Mechanical influences
Fetal head Fetopelvic relationships
Cardinal movements
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Fetal Head: ( a mechanical
influence) Bones: The head is the largest portionof the fetal body, & because it is a firm,noncompliant bony structure, it is the
fetal component that is of mostsignificance (from an obstetricalperspective).
Sutures & Fontanelles: Between thebones of the fetal head aremembranous spaces called sutures.The fontanelles are areas of the head
where suture lines intersect.
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Landmarks: Head is divided intodesignated areas (1) the sinciput or
brow portion; (2) the vertex, or top of thehead between the 2 fontanelles; (3) theocciput or back of the head over theoccipital bone.
Diameters: During birth it is desirablethat the smallest diameter of the fetalhead move through the maternal bony
pelvis. The diameter tht presentsthrough the pelvis depends on theamount of flexion or extension of thehead (attitude).
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Fetopelvic Relationships:
Fetal Lie: refers to the relationship of
the long axis of the fetus, as related to
the spinal column, to the long axis of themother. (vertical lie = most common).
Fetal Attitude: refers to the relationship
of the fetal parts to one another. Fetusis described as being in a state of
flexion or extension.
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Fetal Presentation: The part of the fetal
body that enters (or presents to) the
maternal pelvis. Most common = cephalicpresentation (head first).
Fetal Position: refers to the relationship of
an assigned area of the presenting part
(often called the fetal denominator) to thematernal pelvis.
1. Determine the fetal denominator.
2. Mentally divide the maternal pelvis into 4quadrants (R&L anterior, R&L posterior).
3. Assign a standard abbreviation indicating the
fetal position based on findings of vaginal exam.
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Synclitism & Asynclitism: Asynclitic
refers to a fetal head that is not parallel
to the anteroposterior plane of thepelvis. The head is synclitic when the
sagittal suture lies midway between the
symphysis pubis and the sacralpromontory.
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Cardinal Movements:
Also called the mechanisms of labor.
A series of adaptations the fetus makes
as it moves through the maternal bony
pelvis during the process of lavor &birth.
Influenced by the size and position of
the fetus, the powers of labor, the sizeand shape of the maternal pelvis, and
the mothers position.
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8 Cardinal Movements: (in an anterior
occiput position)
1. Engagement
2. Descent
3. Flexion
4. Internal rotation
5. Extension
6. Restitution
7. External rotation of the shoulders8. Expulsion
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Engagement: the mechanism by which
the fetus nestles into the pelvis.
Also referred to as dropping orlightening.
A fetus is engaged when the biparietal
diameter of the fetal head reached the
level of the maternal ischial spines; knownas zero station.
Leopolds maneuvers: the head is more
difficult to move and less of the head isable to be palpated abdominally after
engagement.
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Descent: describes the process that the
fetal head undergoes as it begins its
journey through the pelvis. Pressure from uterine ctx, hydrostatic
forces, abdominal muscles, and gravity
promote descent of the fetus through the
pelvic inlet and midplane.
Descent is continuous from the time of
engagement until birth.
Assessed by measurements calledstations.
Ranges from3 to +3 station.
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Flexion: the process of the fetal headsnodding forward toward the fetal chestand occurs as a result of descent, thethickening of the uterine fundus, &increased resistance of the soft tissues.
Engagement, descent and flexion tend to
occur simultaneously. Internal Rotation: most commonly the
fetus rotates internally from the occiputtransverse position assumed at
engagement into the pelvis to anocciput anterior position whilecontinuously descending.
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Extension: enables the head to be born
when the fetus is in a cephalic position.
Results from the downward forces ofthe uterine contractions and the
resistance of the pelvic floor muscles.
Begins after the head has crowned and is
complete when the head passes under the
symphysis pubis and the occiput, anterior
fontanelle, brow, face, and chin pass over
the sacrum & coccyx and are born over theperineum.
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Restitution: results in a realignment of
the fetal head with the body, after the
head is born. It is common that as the head internally
rotates to an anterior position before its
birth, the shoulders may enter the pelvis in
the oblique diameter.
This allows the head to turn, but as a
result, the neck twists.
Restitution occurs when the head is free ofpelvic resistance, allowing the head to turn
back until it is again at right angles to the
shoulders.
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External Rotation: After the head is
born & restitution occurs, the shoulders
externally rotate so that they are in theanteroposterior diameter of the pelvis.
This is the largest diameter of the outlet, it
easily allows the birth of the broad
shoulders.
Shoulders are born by first delivering the
anterior shoulder from under the
symphysis pubis and then the posteriorshoulder from over the perineum.
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Expulsion: the last cardinal movement;
consists of the birth of the entire body.
The body usually follows easily after thebirth of the head and shoulders.
The time of birth is often documented at
the moment of expulsion.
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PASSAGE: P # 2
Major pelvic bones include the innominate
bones (formed by the fusion of the ilium,
ischium, and pubis around the acetabulum),
the sacrum, and the coccyx.DIVISIONS:
Pelvis is arbitrarily divided into halvesthe
false pelvis and the true pelvis.
False pelvis: wide broad area btw. the iliac
crests & has no major clinical significance for
L&D.
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True Pelvis: the actual bony passage that the
fetus must traverse during labor and birth.
Shape is a curved axis, not a straight
passage , d/t the diameters & planes of thepelvis.
PLANES:
3 common planes of the pelvis are the inlet(the pelvic brim), midpelvis, and outlet.
A pelvis with an adequate inlet & midplane
rarely if ever has reduced diameters for the
outlet.
The coccyx also has slight mobility, which
increases the available space in the outlet.
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PRENATAL ASSESSMENT OF PELVIS:
Clinical pelvimetry reassures both the
health care provider & the woman aboutthe normalcy of the pelvis.
When any variation exists in the pelvic
structures, it can be discussed &anticipatory guidance given (ex- how to
cope with back aches, back labor, etc.)
Rarely an abnormal pelvis such as trueandroid, guidance may include the
planning for a C/S.
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SOFT PASSAGE THROUGH
MATERNAL SOFT TISSUE
STRUCTURES: Soft tissues of the cervix, vagina, and
perineum must stretch to allow passage
of the fetus through the axis of the birth
canal.
Progesterone & relaxin help facilitate
the softening & increase the elasticity of
muscles & ligaments.
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POWERS: P # 3
Uterine labor ctx. of the myometrium.
Ctx.phase consists of a descending
gradient:
The wave begins in the fundus (greatest #
myometrial cells).
Then moves downward through the corpus
of the uterus. Intensity of ctx.diminishes from fundus to
cervix.
Retraction phase.
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EFFACEMENT & DILATATION:
The purpose of uterine ctx.
1. Accomplish the effacement and dilation ofthe cervix.
2. Facilitate the descent & rotation of the
fetus through the passages.
3. Facilitate the separation & expulsion of
the placenta.
4. Control bleeding after delivery by
compressing blood vessels.
Effacement= the thinning or
shortening of the cervix.
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Dilatation = the gradual opening of th
cervix and is a continued extension of
the contraction-retraction processalready described.
Dilatation and effacement take place
concurrently throughout labor.
Dilatation is assessed by vaginal
examination, and is recorded in
centimeters from 0-10 cm.
H d t ti F th th t
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Hydrostatic Force = another power thatfacilitates the process of labor and birth.
Includes the pressure of the fetus withinthe amniotic sac.
As ctx. occur, the membranes andamniotic fluid facilitates dilation and
effacement. Since the lower uterine segment and
cervix are regions of lesser resistance,
the additional pressure of the amnioticsac is of great importance in promotingthe birth process.
Abd i l F th fi l f
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Abdominal Force = the final power for
labor & birth. Intra-abdominal force.
This power is reserved for the 2nd
stageof labor, after effacement & dilation are
complete.
Maternal pushing, or bearing downeffort.
In the expulsion stage, the ctx.change in
character, & many women begin toexperience an involuntary urge to push.
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POSITION: P # 4
In the last half of the 20thcentury, theposition used most frequently for labor
in the US has supine in a hospital bed.
The most common position for birth hasbeen a lithotomy position.
Limited ambulation of laboring women
resulted from use of continuous fetalmonitoring, routine use of IV hydration,
epidural anesthesia and use of
analgesia.
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PSYCHOLOGY OF BIRTH:
P # 5 The progress of labor and birth can be
adversely affected maternal fear andtension.
Norepinephrine and epinephrine maystimulate both alpha and beta receptorsof the myometrium and interfere with
the rhythmic nature of labor. Anxiety can also increase pain
perception and lead to an increasedneed for analgesia & anesthesia.
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Photo Album
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