Components of Labor1

8/2/2019 Components of Labor1

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COMPONENTS

OF LABOR


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PASSAGEThe passage refers to the

route a fetus must travelfrom the uterus through

the cervix and vagina tothe external perineum


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Two pelvic measurements:

The diagonal conjugate(theanteroposterior diameter of

the inlet)- it is the narrowestdiameter at the pelvic inlet

Transverse diameter of theoutlet- it is the narrowestdiameter at the outlet


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PASSENGER The passenger is the fetus

The body part of the fetus that hasthe widest diameter is the head

Whether a fetal skull can pass dependson both its structure(bones,frontanelles, and suture lines) and its

alignment with the pelvis


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STRUCTURE OF THE FETAL SKULL

Cranium- uppermost portion of the skull, iscomposed of 8 bones

> 4 superior bones- frontal, 2 parietal, and

occipital> other 4 bones of the skull- sphenoid,ethmoid, and 2 temporal bones lie at the baseof cranium

The chin, referred to by its Latin namementum, can be a presenting part


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Sagittal suture joints-2 parietalbones of the skull

Coronal suture- line of juncture ofthe frontal bones and the 2parietal bones

Lamboid suture- line of juncture ofthe occipital bone and the 2parietal bones.


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Frontanelles- significantmembrane- covered spaces,

found at the junction of themain suture lines


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> anterior frontanelle(bregma)- lies at thejunction of the coronal and sagittalsutures

- diamond shaped- its anteroposterior diameter

measures approximately 3 to 4 cm; its

transverse diameter, 2 to 3 cm, closeswhen infant is 12 to 18 months of age


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> posterior frontanelle- lies atthe junction of the lamboidal

and sagittal sutures- triangular shaped

- smaller than theanterior frontanelle


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Vertex- space between the

two frontanelles

Sinciput- area over the

frontal bone

Occiput- area over the

occipital bone


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The diameter of theanteroposterior skull depends onwhere the measurements is taken.

The narrowest diameter(approximately 9.5 cm) is from the

inferior aspect of the occiput tothe center of the anteriorfrontanelle

DIAMETERS OF THE FETAL SKULL


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The occipitofrontal diameter,measured from the occipitalprominence to the bridge of thebase is approximately 12 cm

The occipitomental

diameter(approximately 3.5 cm) ismeasured from the posteriorfrontanelle to the chin


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The anteroposterior diameter ofthe pelvis, a space approximately 11cm wide, is the narrowest diameterat the pelvic inlet

So to be born easily, a fetus must

present a parietal diameter, thenarrowest diameter(approximately9.25 cm)


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At the outlet, the fetus mustrotate to present the narrowestfetal head diameter to thematernal transverse diameter, a

space approximately 11 cm wide


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If a fetus presents theanteroposterior diameter of theskull to the anteroposteriordiameter of the inlet, engagement,or settling of the fetal head intothe pelvis, may not occur


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DEGREE OF FLEXION OF THE FETAL HEAD

Full

Flexion

a fetal head flexes so sharply the hin rests on thechest, and the smallest anteroposterior diameter, thesuboccipitobregmatic, is presented to the birth canal

Moderate

Flexion

the occipitofrontaldiameter will be presents

Poor

Flexion

the largest diameter willpresent


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> it follows a fetal headpresenting a diameter of

9.5 cm will fit through apelvis much more readily

than if the diameter is12.0 to 13.5 cm


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MOLDINGA change in the shape of the fetal

skull produced by the force ofuterine contractions pressing thevertex of the head against the not-yet- dilated cervix

Molding is commonly seen in infantsafter birth


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The overlapping of the sagittalsuture line and, generally, thecoronal suture line can be easilypalpated in the newborn skull

No skull molding occurs when a

fetus is breech, because thebuttocks, not the head, arepresented first


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POWERS OF LABORUTERINE CONTRACTIONS

Origins- labor contractions

begin at a pacemaker pointlocated in the uterine

myometrium near one of theuterotubal junctions


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In some women, contractions appear tooriginate at the lower uterine segmentrather than in the fundus. These arereverse, ineffective contractions, andthey may actually cause tightening ratherthan dilation of the cervix

Some women seem to have additional

pacemaker sites in other portions of theuterus. If so, contractions can beuncoordinated


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3 PhasesIncrement- when the

intensity of the contraction

increasesAcme- when the contraction

is at its strongestDecrement- when the

intensity decreases


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Between contractions, the uterusrelaxes

As labor progresses, the relaxation

intervals decrease from 10 minutesearly in labor to only 2 to 3 minutes

The duration contractions also changes,

increasing from 20 to 30 seconds to arange of 60 to 90 seconds


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Contour Changes As labor contractions progress and

become regular and strong, the uterusgradually differentiates itself into 2

distinct functioning areas:> the upper portion becomes thicker andactive, preparing it to be able to exert

the strength necessary to expel thefetus when the expulsion phase of laboris reached


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> the lower segment becomes thinwalled, supple, and passive, so that thefetus can be easily pushed out of the

uterus As these events occur, the boundary

between the two portions becomes

marked by a ridge on the inner uterinesurface, the physiologic retraction ring


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CERVICAL CHANGES Effacement- shortening and thinning of

the cervical canal

Normally, the canal is approximately 1

to 2 cm longWith effacement, the canal virtually

disappears

In primaras, effacement isaccomplished before dilatation begins


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In multiparas, dilatation may proceedbefore effacement is complete

Dilatation- refers to the enlargement

or widening of the cervical canal froman opening a few millimeters wide to onelarge enough(approximately 10 cm) to

permit passage of a fetus


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Dilation occurs for 2 reasons:

Uterine contractions gradually increase thediameter of the cervical canal lumen bypulling the cervix up over the presenting partof the fetus

The fluid- filled membranes press against thecervix. If the membranes are intact, theypush ahead of the fetus and serve as an

opening wedge. If they are ruptured, thepresenting part serves this same function


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Psyche

Woman s psychologicaloutlook, refers to thepsychological state or

feelings that a woman bringsinto labor

Components of Labor1

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