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Chapter 15Chapter 15

Labor and Birth ProcessesLabor and Birth Processes

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Factors Affecting Labor Factors Affecting Labor

At least five factors affect process of labor At least five factors affect process of labor and birth. Five and birth. Five P’P’s: s: PPassenger (fetus and placenta)assenger (fetus and placenta) PPassageway (birth canal)assageway (birth canal) PPowers (contractions) owers (contractions) PPosition of motherosition of mother PPsychologic responsesychologic response

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Factors Affecting Labor—cont’d Factors Affecting Labor—cont’d

PassengerPassenger Size of fetal headSize of fetal head Fetal presentationFetal presentation Fetal lieFetal lie Fetal attitudeFetal attitude Fetal positionFetal position

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Factors Affecting Labor—cont’d Factors Affecting Labor—cont’d

PassagewayPassageway Passageway, or birth canal, is composed Passageway, or birth canal, is composed

of: of: • Bony pelvisBony pelvis

• Lower uterine segmentLower uterine segment

• CervixCervix

• Pelvic floor musclesPelvic floor muscles

• VaginaVagina

• Introitus (external opening to the vagina)Introitus (external opening to the vagina)

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Fig. 15-7. Female pelvis. A, Pelvic brim above. B, Pelvic outlet from below.

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Fig. 15-1. Fetal head at term. A, Bones. B, Sutures and fontanels.

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Fig. 15-2. Examples of fetal vertex (occiput) presentations in relation to front, back, or side of maternal pelvis.

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Fig. 15-10. Uterus in normal labor A, in early first stage; and B, in second stage. Passive segment is derived from lower uterine segment (isthmus) and cervix, and physiologic retraction ring is derived from anatomic internal os. C, Uterus in abnormal labor in second-stage dystocia. Pathologic retraction (Bandl's) ring that forms under abnormal conditions develops from the physiologic ring.

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Fig. 15-11. Cervical effacement and dilation. Note how cervix is drawn up around presenting part (internal os). Membranes are intact, and head is not well applied to cervix. A, Before labor. B, Early effacement. C, Complete effacement (100%). Head is well applied to cervix. D, Complete dilation (10 cm). Cranial bones overlap somewhat, and membranes are still intact.

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Fig. 15-14. Synclitism and asynclitism. A, Anterior asynclitism. B, Normal synclitism. C, Posterior asynclitism.

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Factors Affecting Labor—cont’d Factors Affecting Labor—cont’d

PowersPowers Primary powersPrimary powers

• EffacementEffacement

• DilationDilation

• Ferguson reflexFerguson reflex

Secondary powersSecondary powers• Bearing-down effortsBearing-down efforts

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Factors Affecting Labor—cont’d Factors Affecting Labor—cont’d

Position of laboring womanPosition of laboring woman Position affects woman’s anatomic and Position affects woman’s anatomic and

physiologic adaptations to laborphysiologic adaptations to labor Frequent changes in positionFrequent changes in position

• Relieve fatigueRelieve fatigue

• Increase comfortIncrease comfort

• Improve circulationImprove circulation

Laboring woman should be encouraged to find Laboring woman should be encouraged to find positions most comfortable to her positions most comfortable to her

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Process of Labor Process of Labor

Labor: process of moving fetus, placenta, and Labor: process of moving fetus, placenta, and membranes out of uterus and through birth membranes out of uterus and through birth canalcanal

Various changes take place in woman’s Various changes take place in woman’s reproductive system in days and weeks reproductive system in days and weeks before labor beginsbefore labor begins

Labor can be discussed in terms of Labor can be discussed in terms of mechanisms involved in process and stages mechanisms involved in process and stages woman moves through woman moves through

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Process of Labor—cont’d Process of Labor—cont’d

Signs preceding laborSigns preceding labor Lightening or droppingLightening or dropping Bloody showBloody show

Onset of laborOnset of labor Onset of true labor cannot be ascribed to single Onset of true labor cannot be ascribed to single

cause. Many factors involved, including changes cause. Many factors involved, including changes in maternal uterus, cervix, and pituitary glandin maternal uterus, cervix, and pituitary gland

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Process of Labor—cont’d Process of Labor—cont’d

Stages of laborStages of labor First stageFirst stage Second stageSecond stage Third stageThird stage Fourth stageFourth stage

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Process of Labor—cont’d Process of Labor—cont’d

Mechanism of laborMechanism of labor Seven cardinal movements of mechanism of Seven cardinal movements of mechanism of

labor that occur in vertex presentationlabor that occur in vertex presentation• EngagementEngagement

• DescentDescent

• FlexionFlexion

• Internal rotation Internal rotation

• ExtensionExtension

• Restitution and external rotation Restitution and external rotation

• Expulsion (birth)Expulsion (birth)

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Fig. 15-13. Cardinal movements of the mechanism of labor. Left occipitoanterior position. A, Engagement and descent. B, Flexion. C, Internal rotation to occipitoanterior position. D, Extension. E, External rotation beginning (restitution). F, External rotation.

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Physiologic Adaptation to Labor Physiologic Adaptation to Labor

Fetal adaptationFetal adaptation These changes occur in: These changes occur in:

• Fetal heart rate Fetal heart rate

• Fetal circulationFetal circulation

• Fetal respirationFetal respiration

• Other behaviorsOther behaviors

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Physiologic Adaptation to Labor—Physiologic Adaptation to Labor—cont’d cont’d

Maternal adaptationMaternal adaptation As woman progresses through stages of labor, As woman progresses through stages of labor,

various body system adaptations cause her to various body system adaptations cause her to exhibit both objective and subjective symptomsexhibit both objective and subjective symptoms

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Physiologic Adaptation to Labor—Physiologic Adaptation to Labor—cont’d cont’d

Maternal adaptationMaternal adaptation Cardiovascular changesCardiovascular changes Respiratory changesRespiratory changes Renal changesRenal changes Integumentary changesIntegumentary changes Musculoskeletal changesMusculoskeletal changes Neurologic changesNeurologic changes Gastrointestinal changesGastrointestinal changes Endocrine changesEndocrine changes

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Key Points Key Points

Labor and birth are affected by the five P’s: Labor and birth are affected by the five P’s: passenger, passageway, powers, position of passenger, passageway, powers, position of the woman, and psychologic responsesthe woman, and psychologic responses

Because of its size and relative rigidity, the Because of its size and relative rigidity, the fetal head is a major factor in determining the fetal head is a major factor in determining the course of birthcourse of birth

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Key Points—cont’d Key Points—cont’d

Diameters at plane of pelvic inlet, midpelvis, Diameters at plane of pelvic inlet, midpelvis, and outlet plus axis of the birth canal and outlet plus axis of the birth canal determine whether vaginal birth is possible determine whether vaginal birth is possible and how fetus passes down birth canaland how fetus passes down birth canal

Involuntary uterine contractions expel fetus Involuntary uterine contractions expel fetus and placenta during first stage of laborand placenta during first stage of labor

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Key Points—cont’d Key Points—cont’d

First stage of labor lasts from beginning of First stage of labor lasts from beginning of dilation to full dilation of the cervix dilation to full dilation of the cervix

Second stage of labor lasts from full dilation Second stage of labor lasts from full dilation to birth of the infantto birth of the infant

Third stage of labor lasts from the infant’s Third stage of labor lasts from the infant’s birth to the expulsion of the placentabirth to the expulsion of the placenta

Fourth stage is first 2 hours after birthFourth stage is first 2 hours after birth

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Key Points—cont’d Key Points—cont’d

Cardinal movements of labor are Cardinal movements of labor are engagement, descent, flexion, internal engagement, descent, flexion, internal rotation, extension, restitution and external rotation, extension, restitution and external rotation, and expulsion of the infantrotation, and expulsion of the infant

Events precipitating the onset of labor are Events precipitating the onset of labor are unknown; but many factors, including unknown; but many factors, including changes in the maternal uterus, cervix, and changes in the maternal uterus, cervix, and pituitary gland, are thought to be involvedpituitary gland, are thought to be involved

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Key Points—cont’dKey Points—cont’d

Healthy fetus with adequate Healthy fetus with adequate uterofetoplacental circulation will be able to uterofetoplacental circulation will be able to compensate for the stress of uterine compensate for the stress of uterine contractionscontractions

Progressing through labor, various body Progressing through labor, various body systems adapt to the birth processsystems adapt to the birth process

When pushing, women should be encouraged When pushing, women should be encouraged to use the open-glottis methodto use the open-glottis method