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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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