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Labor and Birth Processes: 

Labor and Birth Processes Chapter 18

The 5 “Ps” of Labor:: 

The 5 'Ps' of Labor: Passenger (fetus) Powers (uterine contractions) Passage (the pelvis andamp; maternal soft parts) Position (maternal) Psyche (maternal psychological status)


PASSENGER (FETUS): Biological influences A pregnancy that terminates during the 38-42 week gestation is likely to indicate a healthy fetus. Mechanical influences Fetal head Fetopelvic relationships Cardinal movements

Fetal Head: ( a mechanical influence): 

Fetal Head: ( a mechanical influence) Bones: The head is the largest portion of the fetal body, andamp; because it is a firm, noncompliant bony structure, it is the fetal component that is of most significance (from an obstetrical perspective). Sutures andamp; Fontanelles: Between the bones of the fetal head are membranous spaces called sutures. The fontanelles are areas of the head where suture lines intersect.


Landmarks: Head is divided into designated areas (1) the sinciput or brow portion; (2) the vertex, or top of the head between the 2 fontanelles; (3) the occiput or back of the head over the occipital bone. Diameters: During birth it is desirable that the smallest diameter of the fetal head move through the maternal bony pelvis. The diameter tht presents through the pelvis depends on the amount of flexion or extension of the head (attitude).













Fetopelvic Relationships:: 

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 the mother. (vertical lie = most common). Fetal Attitude: refers to the relationship of the fetal parts to one another. Fetus is described as being in a state of flexion or extension.


Fetal Presentation: The part of the fetal body that enters (or presents to) the maternal pelvis. Most common = cephalic presentation (head first). Fetal Position: refers to the relationship of an assigned area of the presenting part (often called the fetal denominator) to the maternal pelvis. Determine the fetal denominator. Mentally divide the maternal pelvis into 4 quadrants (Randamp;L anterior, Randamp;L posterior). Assign a standard abbreviation indicating the fetal position based on findings of vaginal exam.


Synclitism andamp; Asynclitism: Asynclitic refers to a fetal head that is not parallel to the anteroposterior plane of the pelvis. The head is synclitic when the sagittal suture lies midway between the symphysis pubis and the sacral promontory.



Cardinal Movements:: 

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 andamp; birth. Influenced by the size and position of the fetus, the powers of labor, the size and shape of the maternal pelvis, and the mother’s position.


8 Cardinal Movements: (in an anterior occiput position) Engagement Descent Flexion Internal rotation Extension Restitution External rotation of the shoulders Expulsion


Engagement: the mechanism by which the fetus nestles into the pelvis. Also referred to as 'dropping' or 'lightening'. A fetus is engaged when the biparietal diameter of the fetal head reached the level of the maternal ischial spines; known as zero station. Leopold’s maneuvers: the head is more difficult to move and less of the head is able to be palpated abdominally after engagement.










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 called stations. Ranges from –3 to +3 station.


Flexion: the process of the fetal head’s nodding forward toward the fetal chest and occurs as a result of descent, the thickening of the uterine fundus, andamp; increased resistance of the soft tissues. Engagement, descent and flexion tend to occur simultaneously. Internal Rotation: most commonly the fetus rotates internally from the occiput transverse position assumed at engagement into the pelvis to an occiput anterior position while continuously descending.


Extension: enables the head to be born when the fetus is in a cephalic position. Results from the downward forces of the 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 andamp; coccyx and are born over the perineum.


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 of pelvic resistance, allowing the head to turn back until it is again at right angles to the shoulders.


External Rotation: After the head is born andamp; restitution occurs, the shoulders externally rotate so that they are in the anteroposterior 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 posterior shoulder from over the perineum.


Expulsion: the last cardinal movement; consists of the birth of the entire body. The body usually follows easily after the birth of the head and shoulders. The time of birth is often documented at the moment of expulsion.

PASSAGE: “P” # 2: 

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 halves – the false pelvis and the true pelvis. False pelvis: wide broad area btw. the iliac crests andamp; has no major clinical significance for Landamp;D.


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 andamp; planes of the pelvis. PLANES: 3 common planes of the pelvis are the inlet (the pelvic brim), midpelvis, and outlet. A pelvis with an adequate inlet andamp; midplane rarely if ever has reduced diameters for the outlet. The coccyx also has slight mobility, which increases the available space in the outlet.


PRENATAL ASSESSMENT OF PELVIS: Clinical pelvimetry reassures both the health care provider andamp; the woman about the normalcy of the pelvis. When any variation exists in the pelvic structures, it can be discussed andamp; anticipatory guidance given (ex- how to cope with back aches, back labor, etc.) Rarely an abnormal pelvis such as true android, guidance may include the planning for a C/S.


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 andamp; relaxin help facilitate the softening andamp; increase the elasticity of muscles andamp; ligaments.

POWERS: “P” # 3: 

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.


EFFACEMENT andamp; DILATATION: The purpose of uterine ctx. Accomplish the effacement and dilation of the cervix. Facilitate the descent andamp; rotation of the fetus through the passages. Facilitate the separation andamp; expulsion of the placenta. Control bleeding after delivery by compressing blood vessels. Effacement= the thinning or shortening of the cervix.


Dilatation = the gradual opening of th cervix and is a continued extension of the contraction-retraction process already described. Dilatation and effacement take place concurrently throughout labor. Dilatation is assessed by vaginal examination, and is recorded in centimeters from 0-10 cm.


Hydrostatic Force = another power that facilitates the process of labor and birth. Includes the pressure of the fetus within the amniotic sac. As ctx. occur, the membranes and amniotic fluid facilitates dilation and effacement. Since the lower uterine segment and cervix are regions of lesser resistance, the additional pressure of the amniotic sac is of great importance in promoting the birth process.


Abdominal Force = the final power for labor andamp; birth. Intra-abdominal force. This power is reserved for the 2nd stage of labor, after effacement andamp; dilation are complete. Maternal pushing, or bearing down effort. In the expulsion stage, the ctx.change in character, andamp; many women begin to experience an involuntary urge to push.

POSITION: “P” # 4: 

POSITION: 'P' # 4 In the last half of the 20th century, the position used most frequently for labor in the US has supine in a hospital bed. The most common position for birth has been a lithotomy position. Limited ambulation of laboring women resulted from use of continuous fetal monitoring, routine use of IV hydration, epidural anesthesia and use of analgesia.


PSYCHOLOGY OF BIRTH: 'P' # 5 The progress of labor and birth can be adversely affected maternal fear and tension. Norepinephrine and epinephrine may stimulate both alpha and beta receptors of the myometrium and interfere with the rhythmic nature of labor. Anxiety can also increase pain perception and lead to an increased need for analgesia andamp; anesthesia.



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